Can a 16 year old girl get a waxing in the 9 days?
The custom of not cutting hair during Bein Hamitzarim also includes the hair on one’s legs, unless it is needed for extenuating circumstances. This would include shaving waxing and electrolysis. A girl in shidduchim, or a married woman may shave her legs if it is needed. Tweezing eyebrows is however permitted according to most poskim.
Igros Moshe Y:D 2 137, Kitzur HIchos Bein Hamitzarim R’ Eider, in the name of R’ Moshe Feinstein zt”l pg. 4, Hilchos Bein Hamitzarim ( R’ S. Kaminetzsky shlit”a) 6-2,3,4. Emes L’Yackov ftnt. 512, Nitei Gavriel 19 ftnt. 10 in the name of R’ S. Z. Auerbach and Shevet Halevi zt”l.