Me & my girlfriend are both on the spectrum & she feels like nobody truly understands her or loves her for who is really is including me but she thinks I do a better job at it than anyone else does. I suspect I understand & love her more than she realizes sometimes. Cass was raised to be a people pleaser & put others needs first. She feels like a failure when she cant help others & for not being independent like society seems to expect most others be these days. She's her biggest critic sometimes. Since she doesn't accept & love herself for who she is, she does not fully get why anyone else would. It breaks my heart but it's partly due to her own issues & there's only so I can realistically do help. Thankfully she doesn't hate me because I fail, she loves me because I try.
I'm not sure if that's the case for your girlfriend or not OP. My advice that you might already do is to try having conversations with her about her wants & needs when she's in a better mood. The best you might be able to do is to just be there for her & show her you really care & are trying even when she's in a bad mood unless you think it's beater for her to have her space then. Also telling her things you do love & admire about her probably won't hurt but the compliments need to be genuine. I wish I had some better advice here. Hopefully this thread will have more replies.