You guys are crackin' me up
She charged you 75 bucks for a perm, and now she wants the family discount? Oh no. I agree with everyone else. You're time is worth something, and if she doesn't think so I'd tell her to go elsewhere. My guess is she knows your work is good and that she wouldn't get it from anyone else at that price.
OR, you could do them for free and tell her it's her wedding gift