She just doesn't get it, because she's never been treated like a loser freak. Its wonderful that she says she accepts you the way you are (just wait until an Autistic behavior causes her real frustration and see how fast that tune changes), but life is a much bigger picture than one supposedly supportive person saying "It's okay that you're different".
If Opal is right about sigmatizing, it may be that she's afraid of what her friends and family will think if she's with somebody who's been diagnosed with a 'MENTAL ILLNESS'. Let's even put some spin on it: 'NEURO-PSYCHIATRIC DISORDER'. How 'okay' do you think she'll be with that? And if she's not okay with it, then she doesn't really accept you as you are. 'For better or for worse' as it were.
You need to do what's best for you and your self-understanding and peace of mind. Girlfriends come and go.
That bile having been spewed - if she is serious and sincere, and happily accepts you no matter what the diagnosis, that's something special - hang on to that.