When does hair on a women’s body become a chatzitza?
My understanding of your question is regarding the actual hair if it is a chatzitza, and if there is a chatzitza inside of her hair.
Essentially any hair the women doesn’t want, and usually shaves, should preferably be removed before going to the mikva. If she already toveled she doesn’t have to go back to the mikva. She should also be careful that any hair that was cut or shaven, that none of it is on her body. Therefore, she should shave or wax or take a haircut a day or two before the day of the mikva.
Igros Moshe Y:D 2 80, Shulchan Shlomo (Refuah) 3 pg. 11, Teshuvos Vhanhagos 1 -522, Pri Tahara 198- 24, Mareh Cohen pg. 93, 123, Poskim.