welcome to our community!!!
And thank you for sharing with us your question.
Usually the doctor, who is taking care of the treatment has to answer those questions, therefore I do not understand why the doctor cannot answer those questions.
If you tell me which city you are looking for a doctor I can do some research, but be adviced that your girlfriend has to first go for treatment to the doctor and only then he/she will be able to write something for the Ausländerbehörde.
I hope I could assist you and I am looking forward to the specification of your question.