Definately sounds like OCD. There's no real cue as such, but with therapy, it can be controlled, and/or reduced significantly. There was a guy at school with really bad OCD, but he's managed to get over it quite a lot. He says sometimes things still bother him, but he can control it, and not worry/have to change it to how it 'should' be.
The equivalence is relatively common (people who don't have OCD still do it), but I'm not so sure about the being left alone part... She should consult her GP if she's worried, and you can help her by doing anything you can to support her.