The term 'fallen angel' was used to describe women who had violated rules of sexual conduct in the 1800s.

This is a true statement. Considering that women were considered the "fairer sex" in the Victorian Age, it was understandable that they were seen to be "angelic" in nature. When a woman sullied her and her family's name by engaging in sex outside of the marital relationship, it was seen as falling into the temptation of Lucifer, the fallen angel from Heaven.