Francis Knowles, Henry Balfour, J.A. Harley, and Barbara Freire-Marecco in the Pitt Rivers Museum 1998.266.3
During the first world war she met her husband, Robert Aitken, whilst working at the War Trade Intelligence Department. She travelled widely throughout Europe with her husband over the next few years, spending much time in Spain where she continued her anthropological work. She eventually moved near to Stockbridge in Hampshire where she lived with her husband. 
Her obituary in Folklore records:
one remembers her immediately, as a warm, sincere friend rather than as an expert on the Pueblo Indians and the experienced anthropologist. Tall and black-haired, the dignified, kindly expression and the handsome face with its acquiline nose, dark highly intelligent eyes, the musical clear decisive voice, have all left their unforgettable impression on a well-bred, distinguished exceptional woman. As the Hon. Secretary of the Folk-Lore Society ... she was stimulating, efficient and richly helpful. Her quiet scholarly comments on the papers ... were very sound and sprang from a wise experience, an inherited adminstrative background and an astute academic judgment. ... She was a friend to value and to remember.
She was a member of the Folklore Society from 1926 to her death in 1967 and the Secretary of the Society in 1926-1928. She seems to have joined the year she became Secretary. The President that year was John Linton Myres and Balfour was a Vice-President so her old teachers might have asked her to join to be secretary. Her address given in the list of officers of the Society in 'Back Matter' [Folklore, Vol. 37, No. 1 (Mar. 31, 1926)] is care of the Royal Anthropological Institute. She joined the Royal Anthropological Institute in 1907 when she was elected a fellow. From 1912-1929 she was the editor of Notes and Queries in Anthropology. She was replaced in 1929 by L.W.G. Malcolm who also gave an address of the Royal Anthropological Institute.
She published several short accounts of English folklore in Folklore in 1909 and 1910. She wrote many letters, short articles and reviews for the journal between 1926 and 1966. In 1959 she published a paper, 'Relocalization' in Folklore, which starts by referring to an English sense of place:
'Hampshire, that's where they puts the pig on the wall to see the band go by,' say Wiltshire people. But the writer of an article in The Times (9 November, 1959) reports this as a Midland quip about folk in the Black Country. [Aitken, 1959: 546]
In the rest of the article she discusses what 'governs these processes of localization and relocalization' with reference to field data from Spain. She concludes:
The condition for localization - congruity
The motive - sometimes, but by no means always, personal or local advantage
The process - sometimes deliberate adoption, But always? [Aitken, 1959: 549]
Freire-Marreco gave a total of 845 artefacts to the Museum. Her first artefacts were given in 1905, the year she first started studying in Oxford. These included ear-plugs from Zanzibar and a Moorish hashish pipe. Her last artefacts were given in 1962, some family heirlooms (lithographs and paintings) that had belonged to her grandmother. She funded her first period of fieldwork by selling a collection to the Pitt Rivers Museum that she had acquired in New Mexico and Arizona [1911.86] Her artefacts come from a wide number of countries: Canada, China, Congo, Cyprus, England, France, Germany, India, Ireland, Italy, Mexico, Montenegro, Morocco, The Netherlands, Nigeria, Poland, Portugal, Russia, Spain, Tanzania, Turkey, Ukraine, United States of America.
She gave a total of 5 artefacts from England to the Museum:
1908.38.1 Leaden pilgrim-bottle found on the undercliff at Southwold. (her address when she gave this item is said to be Potter's Croft, Horsell, Surrey).
Detailed Amulet card catalogue entry - Amulets D. Crop Fertility, E. Offerings to Gods etc F. Spirit Houses, Scares G. Sacred and Mem. food H. Relics and Mementos - Pilgrim badges and mementos Description: A pilgrim's bottle of lead, found with others on the undercliff at Southwold. Locality: Southwold [insert] Suffolk [end insert] How Acquired: Pres by Miss B Freire Marreco 1908 [ironically, she wrote this catalogue entry herself)
1908.38.2 Specimen illustrating loop-weaving through a bobbin, English.
1910.6.2 Sacral bone of a rabbit mounted as a pin, the natural form suggesting an animal's head on either side has been accentuated by inserting eyes. Locality not known, bought in London.
1954.6.13-14 Photographs of a young man and of a man and a woman. Taken in London in 1924 when they were appearing in the "Covered Wagon" film.
Freire-Marreco was one of the first Oxford students to have been taught by Balfour for any prolonged period of time. In his 1905 annual report for the Museum, Balfour noted that Freire-Marecco had undertaken ‘a course of study in Prehistoric Archaeology under my direction during the Summer Term’. She continued her studies with Balfour the following year, and in 1907 was one of the first students to be admitted on the new Diploma course. She kept in touch with Balfour over the years (although only a couple of letters, one undated and the other dated in July 1918, survive in Balfour’s papers at the manuscript collections of the PRM). There are also some postcards from her to Beatrice Blackwood in the Blackwood manuscript collections. [Blackwood General Correspondence A-D : Envelope A 1-25] Although Blackwood had taken the Diploma much later than Freire-Marreco, she had followed in her footsteps, doing research in the Acoma pueblo in 1926-7. The only specimen recorded as part of Balfour’s collection, collected by Freire-Marreco and given to him as a personal gift, was an example of cedar bark tinder from Arizona, given to him in 1913.
 This information was provided by Chris Wingfield from the list of attendees at Edward Burnett Tylor's lectures, held in the PRM manuscript collections.
 Much of this biographical information was provided by Claire Warrior of the National Maritime Museum, while she was researching Freire-Marreco's North American collections at the Pitt Rivers Museum.
 She tells quite an amusing story during this article:
A certain English village provides two more instances. A doctor (now deceased), a man of high intelligence, complete integrity, long local experience, and not given to leg-pulling, told before 1939 the following story.
Old J.W. (a respected local tradesman) was on his deathbed, his household gathered round him. 'Are you there, Hal?' he asked feebly. 'Ye, father, I'm here.' 'Are you there, Bob?' 'Yes, grandfather, I'm here.' 'Are you there, Hannah?' 'Yes, Mr W--, I'm here.' 'Are you there, Mrs Jones?' 'Yes, sir, I'm here.' 'Are you there, Janey?' 'yes, uncle, we're all here.' The old man, sitting up and in a loud voice: 'THEN WHO'S LOOKING AFTER THE SHOP?' [Aitken, 1959: 548]
Lake, E. F. Coote. 1967 'Barbara Freire Marreco (Mrs Robert Aitken)' Folklore Vol. 78, No. 4 (Winter, 1967), pp. 305-306
Aitken, Barbara. 1959. 'Relocalization' Folklore Vol. 70, No. 4 (Dec., 1959), pp. 546-549
Aitken, Barbara. 1966. 'Surrey Peat' Folklore Vol. 77, No. 1 (Spring, 1966), pp. 67-68
Freire-Marreco, Barbara. 1909 '63. Notes on the hair and eye colour of 591 children of school age in Surrey' Man Vol. 9, (1909), pp. 99-108
Freire-Marreco, Barbara. 1909 'Scraps of English folklore IV' Folklore Vol. 20, No. 4 (Dec. 30, 1909), pp. 488-491
Freire-Marreco, Barbara. 1910 'Scraps of English folklore V' Folklore Vol. 21, No. 2 (Jun., 1910), pp. 222-227
There is a biography of Barbara Freire-Marreco, A life well led by Mary Ellen Blair, published in 2008 by Sunstone Press. The synopsis on Amazon.co.uk says:
What would inspire a proper young British woman, well-educated and devoted to the Church of England, to venture forth from a sheltered academic life of the early 20th century to cross an ocean in order to conduct investigations on a people that she considered "uncivilized?" To answer this question, the author collected Barbara Freire-Marreco Aitken's correspondence, most of which has never been published, and with editing, annotating, and researched explanations completed the gestalt resulting in a biography that is a cohesive and interesting adventure story. This remarkable second generation British anthropologist lived with Native American pueblo people and visited reservations in the Southwest United States, contributing to the knowledge about and understanding of these people. The dearth of exposure of her experiences makes this a long overdue compilation of her life and work. Even those with little interest in her focus of anthropology and ethnology will find this life story interesting because of the period of time in which she lived, especially because she was a British woman in territory that only recently had become part of the United States.