I used to cut Belle's nails when I first got her at 12 weeks. She was really good and I played with her feet all the time. Then she decided she didn't like me cutting her nails and she's cry and pull away. I didn't let go and got the job done but found it much easier if my DH held her tight against him and I just grabbed a foot and cut. Fast and easy. Belle started the growling and nipping at me when I would groom her, especially if she had a snarl in her fur. I always grabbed her face by the furnishings and looked her in the face and said no bite and waited until she looked away first. She has bitten at me a couple times but she was aiming for the brush. She still got the same no bite and now she knows better. It can be a battle with some dogs but if you let them win, you'll never be the alpha.
A dog that bites is totally unacceptable
Just be strong and don't let her sense any weakness. Good luck, keep trying, you'll do fine.