The pose this woman takes in her portrait is amazing, especially considering the time at which it was painted. It's very daring!
Indeed, it was unusual for a woman to pose that way in the 1870s. You could easily contrast it with other images of women in that gallery like women looking off to the side, sitting quietly, looking as if they were waiting to be looked "at."
The sitter is an actress named Sarah Cowell. According to a book from 1908, she was a New Yorker who made her debut in a theater on Union Square in 1878 (a year after this painting was made). She also performed in England. She was especially known for performing works based on the writing of the poet Robert Browning. She was married to a man named William Lemoyne, and she continued to perform after she was married, also bold! A final interesting fact about this is that is was painted by a woman -- these were women with professional ambitions.