The way I look at it, what you were diagnosed with is nothing that would change who you are in her eyes. It's just some words added to the person she already knows. You've been that all along. You've been that when she met you, and when she decided she wants to know you better, when she started liking you. You are still the same you. I don't see how the revelation could scare her away, but I can imagine how they may help her understand you better, provide more reference and maybe explain some things about you that she found puzzling.

Yes, revealing your secrets feels scary. What if the other person freaks out - it's not impossible to imagine, but so very, very unlikely to happen.

These conditions get a lot of positive representation in popular culture (Monk comes to mind for OCD), and even if you find portrayal incomplete or not realistic enough, they do remove fear of the unknown and prepare us to be more compassionate fellow travelers.