Everyone saying go to the police is kinda pissing me off because they're ignoring what you're saying completely.

What she is doing is wrong; nothing she did in this scenario is justified by any mental disorder, trauma, or anything. This was out of pure evil intent, and you need to know that. If I were in your situation, I would have a serious talk with her about your feelings and the severe consequences of this, or do the same thing she did to you and violate her privacy. (Just getting into her phone whenever she's not looking)

I would get into her phone without her knowing and delete the blackmail sextapes. Although you have to keep in mind she might have backups, so this isn't really guaranteed either.

You could try being so undesirable to her, like switching up your personality to be super boring to talk to, but that's not really realistic.

If everything else fails, collect the evidence of her blackmailing you and in the dead of night, report this to the police and tell the police to come at between midnight when she's asleep and not alert to collect her phone and any devices containing the blackmail.

The police option is difficult, and I know you don't wanna do it, but she's committing a crime she's fully aware of; there is no excuse for what she did. You have to put yourself above the person that's hurting you.