Sounds like your therapist probably shouldn't have extended texting during her medical leave. While it was kind to offer, considering the extent of the illness and surgery, it was probably very unrealistic on her part to think she could deal with clients during her recovery from such an extensive surgery and illness, particularly if the amount or content of texting has become problematic.

Sometimes we just don't realize how difficult things will be when dealing with a medical issue. It sounds like that may be the case for your therapist. I hope you can find a way to understand that your therapist needs to take care of herself right now and is having to put this boundary in place for her own health and well-being.