Dealing with Dog on Dog Aggression?

I'm really worried. I have a Great Pyrenees and she was never aggressive. About 2 years ago she had her first litter of two puppies. She did become overprotective, we couldn't get to near her or the pups. The crazy thing is that the dad of the pups wouldn't approach her or pay attention to her and she would want to attack him even if he was really far away. We moved her into the garage while the pups grew and eventually she let us get close until finally we moved them to the back. We have given the puppies away, although my dog has not been the same since then. She hasn't gotten pregnant anymore because she became too aggressive, she would attack my other dog on sight for no reason. I don't know why, and I don't know what to do because I don't want to put her down. But just recently she attacked him again, take in mind that the male dog is older now so he doesn't do much damage, she would not let go of his neck and hurt his leg. I just don't know what else to do.