Question:
Is it permitted for a single girl (not in shidduchim) to shave her underarms or legs during sefira?
Answer:
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.
Best Wishes
Sources:
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,