With her expertise, technical skill and patience in handling animals in front of her Rolleiflex camera, Ylla photographed a wide variety of animals in her studio – dogs from animal homes, a little lion, kittens, or also a squirrel - the main character in the book Tico Tico (Harpers & Brothers, 1950). Often, she kept the animals for several days in her studio, to study their behaviour and devise tricks in order to capture them photographically in unusal and often amusing ways. Her first studio (and residence) was at 15 West 51st Street in Midtown Manhattan, the same street where the German émigré photographer Lotte Jacobi lived. From around 1946, her studio and residence was at 200 West 57th Street, close to Central Park and the Central Park Zoo, as well as to other studios and galleries, such as the Norlyst Gallery and Weyhe Gallery. In 1942 Ylla’s photographs were presented in two exhibitions at the Weyhe Gallery: in February, she participated in Animals and in November she took part in a show on the topic of cats (Anonymous 1942, 11–12; The New Yorker, 21 November 1942, p. 4)

Beside photographing the animals in her studio, Ylla sometimes took them to Central Park to photograph them there. Furthermore, she also found some of her models in New York Zoos. Ylla already did photo sessions in European Zoos before her emigration to New York as can be seen in the image Back to Methusala, which was published in U.S. Camera in 1943 that shows a turtle in the London Zoo at Regent's Park. For "Babytime at the Zoo" reportage (Life, 15 May, 1944) she contributed five pictures taken at Bronx Zoo. Photographing animals is not easy, but Ylla's subjects' expressive and often funny poses clearly show her technical skill, experience and patience in handling animals in front of her Rolleiflex camera. For her "Ylla's camera tells. A tale of two kittens." series published in Popular Photography in 1951, she took the outside photos in Central Park (Ylla, 1951). Also for animal photographer Lilo Hess, the New York zoos were important urban locations for outdoor images. As images in Lotte Jacobi’s archive show, also the émigré photographer visited the zoos frequently in New York and made images there. Beside reportages Ylla's photographs were also featured on the cover of magazines as Life, Popular Photography and U.S. Camera. As cover images were a highly valued goal for photographers, this gave her a high reputation as animal photographer in the American and international press.  

Ylla's work was represented by the Rapho Guillumette photo agency, re-founded by the emigrant Charles Rapho in 1940. The agency already run in Paris in 1933 as Rapho by Charles Rado (Rapho stems from Rado + Photo). When Charles Rapho moved to New York the agency became Rapho Guillumette, in partnership with Paul Guillumette. Besides magazine contributions, Ylla successfully published children's and animal books in various languages with publishing houses in the U.S., Great Britain, France and Germany. Among them were They All Saw It (Harpers & Brothers, 1944), Dogs (Harpers & Brothers, 1945) and The Sleepy Little Lion (Harpers & Brothers, 1947). Most of her books were translated into different languages. In the 1950s she published several books on her travels, such as Animals in Africa (1953, Harpers & Brothers) and Animals in India(Harper’s & Brothers, 1958).

Even before her emigration to New York, Ylla had contributed her animal photographs to publications such as Animal Language in 1938. This photobook was a collaboration between the biologist Julian Huxley, the bio-acoustic expert Ludwig Koch and Ylla. In 1950, she again collaborated with Julian Huxley to publish the photobook Animals.

Born as Camilla Koffler, she was a successful photographer in Paris and London before emigrating to New York. From 1931, she ran an animal photography studio in Paris. Her empathic and humorous eye-level interactions with animals found a wide audience. From Paris, where she was represented by Rapho Guillumette, she cooperated regularly with London magazines such as Lilliput and Zoo Magazine. As correspondence in the archive of Fred Stein testifies, the two photographers knew each other from their first exile stop  in Paris and maintained their association in New York. An article on the photographer Fritz Neugass reveals that Ylla left Europe on 6 May, 1940 on board of the S.S. Winnipeg, along with other photographers including Fred Stein, Josef Breitenbach, Charles Leirens, Ilse Bing and Yolla Nicholas. In 1947, Ylla she became a U.S. citizen.

During the 1950s Ylla began long-distance trips to India and Africa, to create animal photographs for new photo books, such as Animals in Africa (Harpers & Brothers, 1953). Cities and places in Africa she visited where in Kenya the Nairobi National Park, Tsavo National Park, Amboseli National Park and Masai Plains Reserve as well as in Uganda the Kasinga Channel, Lake Victoria, Lake Nakura, Lake Albert, the Nile, and Murchison Falls. In 1954 Ylla traveled to India at the invitation of the Maharajah of Mysore. Further destinations in India were New Delhi, Trivandrum, Mumbai, Saurashtra, Cooch Behar, Assam, Benares and Bharatpur. On May, 30 1955 Ylla died, at the age of 43 during the photographing of a bullock-cart race in Bharatpur.

Ylla is one of the first female photographers who captured animals in their natural environment and behavior. Photo books, such as The little elephant (Harpers & Brothers, 1956), Animals in India (Harpers & Brothers, 1958), Animal Babies (Harpers & Brothers, 1959) and Polar bear brothers (N.Y. 1960) were published posthumously.