grace - what the hell, will stop being cowardly and post.
I became ill with OCD fairly suddenly, at 16, although in retrospect some traits were there beforehand. I had two pretty bad years, and things started to resolve themselves when I left home for university. I think in my case a really quite unhappy life situation was a big contributing factor, but please don't think your dd's OCD is your fault in any way - it can happen independent of any life situations, and really the fact you are posting and care so much about her and wanting her to be happy and do what's most helpful for her indicates to me that she's very lucky to have you as her mum.
My parents, of course, were devastated and at an utter loss; but the way they went about things - breaking into the bathroom, shouting, threatening me with getting me sectioned - was of course counter-prosductive. (In fact, the threatening with sectioning made nme scared enough to refuse therapy altogether, which was obviously not ideal). If I was interrupted in what I suppise I have to call my rituals, I had to start them all over again, as at my worst I really felt I couldn't trust my memory, my mind, to be sure I had done what was necessary. Writing years after, I described it like this: '[my] memory fell off the chronological cliff for seconds on a regular basis, leaving me condemned to repeat the action I had intended as many times as it took my drenched and hanging-on-for-dear-life memory to accept it, haul itself up and dry off [...] I invested in disinfection, placed my little capital in the power of keeping pure. I drank water diluted with vinegar; I measured childproof caps of own-brand pine disinfectant into the bathtub and held my legs in the off-champagne warm water [...] I mourn the strength I was forced (forced?) to give to the hunt for ways and means to sneak back into the now-unlockable bathroom. For this weakness, too, I despise myself: for the power of my compulsion, power it accumulated at throttlepoint, like a local thug collecting protection money. [...] Not daring, for a long time, at least, to stand in its way, to build a barricade, to stage an uprising, I gave it strength, and strength, and strength, selling my future to my present, my eyes bent to the greenish layer of Shield soap on my hands, leaving smudges of foam to indicate I had indeed been there, pushing away the thought of how easy it would be, in another universe, to turn my back on all this.'
In other words - if she experiences it like me - she will probably have some awareness of the actual unnecessariness of the rituals; but the alternative will just be too frightening - at the moment. This is where CBT can be tremendously effective - in appealing to that awareness and strengthening it. Probably techniques such as so-called autogenic training, or visualising the anxiety as a graph whose curve will fall eventually, could help her too.
FWIW: I believe that the potential for OCD is common to all humans, in that we all cling to ritual and structure to make sense of life and feel safe. In OCD that need is greater and that production of ritual and structure - at its core an essential impulse for survival - is more extreme.
Hope some of this helps.