Congrats on getting into USC! I know about controlling mom's too. Mine still tries to boss me around and I'm 25.
If you're mom is going to help pay for vet bills, I would let her tell me what to do too.
Your instincts are right about wanting to walk away. I would. Bargain puppies aren't so much of a bargain in the long run. Kaji was a bargain pup and it looks like I'll be spending a few grand on LP surgery in our future. Not so much of a bargain now right? I love him the same, but it really is something to consider. Check the YTCA page for breeder referrals. Good luck.