First of all, I'm not understanding. Are you wanting to break things off because you're anti-social disorder or because you don't like her? Or both?

Honestly, i'd say join a good support group for your anxiety, social disorder. Even an online one can be fantastic! I have been a member of an online support group for a condition I have -- Misophonia or "4S" or "sound sensitivity." I had little choice for support groups since there aren't any for this condition anywhere near my area. So I can tell you a group who's understanding even just via messaging is so helpful! Whether you want to stick with her or not, I still say you should look into the group to maybe help relieve some of this anxiety.

The best way to break things off with her without hurting her? Tell her about your personal issues. Really. She will understand those far better than the "it's not you, it's me" line or better than "I just want to be friends" Be honest with her and tell her you feel you can't go further into the relationship because of these anxieties and that you'd worry about putting pressure on her too. That will be a good way to break it easily. She won't be as hurt or take it as personally. This is if you still want to remain friends. Tell her and say you just want to take it down to a more friend-only level so that you're able to work through your issues at your own pace without putting loads of stress on you both. Surely she'd still be your friend then. But if you're not wanting to stay friends with her anyways, you may just have to tell her that it's because you're not interested. If so though, just try to tell her you need more personal time to work through the anxieties?

Hope this was at least somewhat helpful. I personally think something along those lines would do well.