[MindieRose]

With a fever, even low grade, rapid breathing is normal, as it is with people. Its the bodies way of trying to cool itself, similar to panting.
Her temp may have been low before if she wasnt drinking a lot from not feeling well. If an animal or person is not feeling well, they tend to not feel thirsty. If you become dehydrated, your body has a hard time maintaining normal temperature. So even if she had been fevered before, if she became dehydrated, she could become hypothermic.
This happened with my daughter when she was on antibiotics. She had such severe diarrhea as a side effect, that she quickly dehydrated and her temp went down to 95 rectally. I rushed her to the er and she had to have IV fluids.
Be sure to push lots of fluids with her as much as possible, especially with her lactating.