Well, though she is no longer getting worse, I fear her improvement has stopped as well. She seems to be losing weight, and just the other day I found little tiny bugs on her. I quickly checked all the other animals in the house as well as the food and bedding, and I still have NO idea where they came from. I spoke to my vet he said they could be one of a thousand opportunistic parasitic insects that prey on sick or injured animals, and the other rats would have easily groomed them off. Ugh! The vet seems to think that perhaps she has some kind of tumor or other brain issue, as she hasn't fully recovered. I'm going to make an appointment to take her in next week.
She seems in good spirits, is as active as she can be (chewing on cardboard, nesting, etc). She's also eating and drinking regularly. I don't know if she'll ever fully recover, but I do hope so.