is it permitted for a single girl (not in shidduchim) to shave her underarms or legs during sefira?
If she is not of marriageable age she shouldn’t, but if she is, then according to some poskim it is permitted for her to shave her legs.
Kovetz Halachos (Sefiras Haomer 10-2). Nitei Gavriel ( Pesach) 49-13,14, Piskei Teshuvos 493-7, R’ Eider (Hilchos Pesach pg. 330) in the name of R’ Moshe Feinstein zt”l,