Her account was not "stolen", she gave it away. This isn't on AdSense (YouTube has NOTHING to do with it), it is on her and a costly mistake. It's unfortunate, I feel for her, it sucks, she seems like a nice girl, but, well, welcome to the world of business.
I’m so sorry to hear that and my heart breaks for you. They’re more than capable to fix the issue. They just don’t tend to care unless you’re a big name. I had issues with being bullied and someone making a channel to mock me, YouTube did nothing for me. I hope they help you.