Mary Florence Daly was appointed as assistant in the Albany Museum, Grahamstown, in 1898, taking over some of the duties of Frank A.O. Pym*, who left to become director of the King William's Town Museum. She soon worked mainly in the museum's herbarium and started collecting plants, though in 1902 she also collected small insects with another assistant, Miss M. Sole*. By 1903 she had added some new species to the list of the flora of Albany that the museum's director, Dr. Selmar Schönland* planned to publish. The next year she collected a fair number of interesting plants on a trip for the museum to the neighbourhood of Sidbury (some 40 km WSW of Grahamstown). She became first assistant in botany in 1905, when Miss E.M. Cherry* was appointed as second assistant. Soon she was able to identify most of the plants brought in to the museum by the public and by 1910 Schönland stated in his annual report that she had a good working knowledge of the flowering plants of South Africa. During 1911 she collected plants for the museum at Humewood, Port Elizabeth. It seems that a sister of hers also helped out in the museum at one time, for in his report for 1912 Schönland experesses his appreciation for "the good and steady work done in the Herbarium by the Misses Daly". Mary Daly married James Head Heny in April 1913, at which time she stopped working.
There are specimens collected by her also in the Compton Herbarium, Cape Town. The species Albuca dalyae was named in her honour by J.G. Baker, of Kew Gardens in 1903.