Q. Can a woman remove facial hair during the 3 weeks?

A. Pri Megodim (551: 3) rules that the prohibition of cutting ones hair applies equally to women as men.
However, in regards to a woman removing facial hair, Nitey Gavriel (Bein Hametzorim 1: 21: 3) rules that women are allowed to remove bodily hair for maintaining her attractiveness to her husband.
Horav Shlomo Millers Shlita opinion is that a woman’s removal of facial hair, should be done before the beginning of the nine days. (See similar opinion on question 102 in this forum, in regards to a woman dying her hair)

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a