How do i get my dog's breath to smell better?

My dog has something wrong inside her i think. The vet says it won't hurt her or change her or anything, but it makes her breath smell REALLY bad. I've tried using the dogs toothpaste to brush her but she won't open her mouth So what can I use to freshen her breath? I've tried everything i can think of, including dentastix and doggie breathmints.