She called him out for making inappropriate sexual comments online to someone she knew, who was 15 at the time. He ended up getting banned. This caused this man to develop a spiteful obsession with her because according to him, she is slandering him as a pedo.
A few months ago he found her social media and his obsession is now in full force. He's boasted about mass reporting her, making false accusations against her, and replying to irrelevant Tweets with accusations in an attempt to stir up drama. She didn't even mention him or talk about him, he just replied to random Tweets with confrontations and when she refused to engage, he replied again using his sockpuppet accounts agreeing with his own reply. He's also said that he's downloaded her photos to his computer (including ones that are a year or two old) and uploaded them to a porn site. She doesn't wear makeup so it's immediately obvious just by looking at her photos she's under 18. When people confront him he uses DARVO tactics. On some sites he's on he pretends to be civil but on his own site his motivations are much more clear. Several individuals in his friends group have allegedly either owned or defended CP.
The lengths he'll go to in order to find every social media she has is insane and based on his post timings he's often staying awake all night to do this.
And yes, she has reported him, but sometimes the moderation is useless and he's very good at using DARVO to try and make it seem she's the one harassing him. He's also using sockpuppet accounts to make it seem like multiple people are making the same accusations when really it's all just him.
https://en.wikipedia.org/wiki/DARVO