Right, see how far I get (typing one-handed and guests due any minute).
Leaping on her is not a good idea, from a psychological but also a practical point of view - when I was leapt on (by angry/hysteriocal/frightened parents) it 'interrupted' what I had to do and afterwardas I had to sneak off, under unbelievable levels of stress, and do it all again. It will not 'shock' her out of it - at least it is unlikely to. Think, for example, about CBT (which it might be worth looking into if this does seem to be a real problem) - it needs several sessions of gradually building up 'exposure' to the anxiety.
My OCD reduced very, very markedly in severity when I left the situation that was causing me a great dealö of stress, which in my case (I was 16/17/18) was a combination of home and school. You need to look at/talk to her about what's happening in her life - calmly. See if you can identify any 'flashpoints'.
Threadworm's point is excellent. Before the OCD I had an episode of anorexia. It didn't last long but I remember being, for the first time ever, very apathetic - partly due to the lack of nutrition, of course, but it was also the mental energy going into it. And OCD is immensely tiring too.
She doesn't have 'two' sides. It's likely her 'good' side and her 'OCD' (or whatever) side are two sides of very much the same coin. Sensitivity and brightness sometimes coexist quite naturally with conditions like these (as they are, in many ways, very basically 'thinking too much'). Please, please don't see it as a flaw which spoils everything else. That was how my parents saw me - and made it clear. Try and see it as simply a part of her right now, and concentrate any dislike of it on the fact that it is stopping her feel happy in and confident of herself.
TC is spot on with her point no. 1. Humans need to control and order the world, and OCD is a way of ordering the world. It - or rather the rituals that emerge from it - provides structure, something to hold on to. At my worst I literally felt like I couldn't trust my own memory. This goes back to what I said about the 'flashpoints' - what/where are the situations in which she might feel out of control, like she needs something to hold on to?