I know you don't want to mention it to your boss, but you would actually be doing her a favor to do so. If he is aware of her diagnosis, if she does have one, he can gently talk to her about professional boundaries and coach her on more appropriate workplace behavior. It doesn't really matter if she has a diagnosis or not, and we really shouldn't try to diagnosis people over the internet as none of us are doctors or know her personal medical and psychiatric history, but there is no reason you shouldn't simply bring this to the attention of your supervisor just as you would if you didn't think she had a disorder. The behavior is not excusable simply because mental illness is involved.

As someone with a disorder who works full-time, if a co-worker has an issue, I do not mind if they feel they need to bring it to the supervisor's attention rather than confront me directly. Especially if they are unsure how to do so. Also it is helpful to ask the third party to intervene to keep things calm.

I wouldn't feel so worried to talk to your boss about it. I would phrase it as kindly as possible when you talk to your boss. You could even mention that it gives you anxiety, so as to frame it in how it is affecting your work performance to have a coworker invading your personal space.

Good luck!
Seesaw