Is it permitted for a woman to shave underarm hair during sefira, to prevent discomfort?
The minhag is that even women do not cut thier hair or shave during sefira. There is a heteer for women to shave when it is l’tzorech mitzva, for a mitzva need, such as going to the mikva or if it will be unsightly to her husband. Othewise she should not shave.
Nitei Gavriel ( Pesach) Chap. 49-2, Ohr L’Tzion 3 Chap 17-4, Piskei Teshuvos 493-7, Kovetz Halachos (Sefiras Haomer) 5-1,2.