I think contacting her would be misinterpreted as “still interested” and would be self-serving on the OP’s part. You don’t want to help her or fix her, you want to be the Good Guy. The Rescuer. The Knight in Shining Armor. Go find someone who is more emotionally healthy to role play with.
All the usual disclaimers: this is really none of my business; I’m sure not qualified to give advice; compared to some of my decisions, the worse-case scenario of your situation would looks like this , etc., but if you were happily involved in a new relationship, would this thread even exist?
Well no - because I wouldn’t be active on a dating website. 
I think that’s the answer right there. I think I initially wanted to check in because my default is to make sure the people around me are happy. But she’s not around, nor do I want her around (simply because the relationship is over - not because she’s toxic or anything). Anything I do would be for my own piece of mind so that I can say, “well, I tried to lend a hand” if she does go completely off the rails.
[Snip & bolding mine]
She sounds a little psycho. And that’s fine.
I think you shoould ignore her. And that’s also fine.
Everything is fine.
Munch, you show a good moral and ethical impulse. Direct that at the next woman, and your ex can get her support from the next guy. (You do get good advice here, and the no’s have it–heed that).
ignore her, move on with your life.
What she does now is really none of your business. Just let it go and try and find the right lady for you. You can’t save anyone from themselves.
Why the fuck does it matter that this is an ex? Someone tried to rape her. He knows about this. It is thus his obligation to do something about it.
What boggles my mind is those of you trying to moralize your way out of it. The only way doing nothing is moral is if you buy the Ayn Rand bullshit that you only look out for others’ interests if it helps you. And I thought we were better than that.
It’s not about being a knight in shining armor. It’s about doing what is right.
I’m not going to come right out and accuse the rape story of being a lie. If the story’s true then it’s horrible. But let me just say that she’s exhibiting a pattern of attention-seeking that I’ve seen before. As Lisa said:
I’m going to disagree with everyone else’s advice here. I don’t see any harm in sending her a note saying something like, “Hey, ex, some of your posts appeared on my news feed [or whatever it’s called], and it sounds like you’re going through a difficult time. I’m not interested in restarting our relationship, but I wanted you to know you can talk to me if you need to.”
Sometimes just knowing there’s someone out there who will spend a little time listening to you can be a lifesaver.
Definitely check in. She sounds like she’s having a tough time and needs support. I don’t think she can rely on you for that long-term but she needs to know someone gives a shit.