Well first off you need to take a deep breathe and get your chihuahua to the vet. She will need an abortion, the puppies are too big for her and will kill her. Second off you will need to get her checked out because the male pit probably ripped her or injured her very severely. And then I would suggest you get her spayed. Don't let this happen again. Keep a eye on your chihuahua so this doesn't happen again. They are too small for big dogs and it will kill her.
I would definatly take her to the vet, and have her checked. They could do a spay now that will abort the puppies. The best thing you could do for her. There is an extremly good chance that the large puppies could kill her, and there is no way they would be able to be born with out a c-section. that could cost you $1000 or more. The other possiblity is that she is able to carry the pups until they get big and then go into labor. The pups could be extremly premature, and die on your or be still born. My boss had a litter taken early due to an infection in the mom. when they went to wipe off the puppies after delivering them, their skin came off. It was horrible. Think about your dogs life.