Hi 2young4this, good to meet you. It is really hard to exercise when you are in pain, no doubt about it.
For myself, gentle exercise is really important to help control my symptoms. It seems counter intuitive, but when I feel myself starting to get really tired and the pain gets bad (for me it is mostly in my hands) a 10 minute walk can restore me. I don't need to walk fast or get my pulse rate up, just move around a little.
As for weight bias, it is certainly possible. Sometimes discrimination is a conscious choice, but more often it is caused by implicit bias the person is not even aware of.
Here is my 2 cents, for what it is worth... You might be able to bypass whatever biases your doctor has by making an agreement with her as to what goals you are trying to reach with your treatments. Then keep a log of treatments and symptoms. By keeping your focus on the goals and your results you can keep her from being distracted by weight bias, or you draw the prejudice out into the open where you can see it clearly.