You are dwelling too much on it. She spoke out of competiveness, ego. And what's wrong about what she considers fit? Others people criteria not always match with our own criteria, or even medical criteria lmfao she was rude, definitely, but the best course of action is what your bf did, not giving her attention. Don't put this on your bf and don't let it damage your relationship.

Don't let that comment get through you, if you let it, then yourself is validating the dismiss of your efforts on the matter, meaning you are questioning the efforts you put on your body.

You don't even care about whatever she has going on with her life, then why would you care about her criteria about what being fit constitutes? Or are you baffled at her rudeness? Is really that kind of rudeness any worth of your time and attention?

Now I must say, if your bf has a background of not protecting you as you would like to, then I think you have reason to be worried in that regard, and so you must communicate with him about this.