Hi OP - so sorry to hear this has all happened. Long reply so no rush, enjoy your much needed chill time and read this when you're ready ❤️
As I've mentioned, I have OCD too and from experience, here's my advice: don't start what WILL become a lifelong habit of giving in every time she claims to feel triggered and claims to have found the 1 thing that will fix it. OCD generally begins much earlier than the timeline she has suggested - this was almost certainly on the cards way before her teens. And it can have many roots, which she's yet to properly explore in therapy, and no matter what, it rarely roots in one person. And there is no 1 thing you can do to get better - recovery is a multi layered process and a long journey. She will not get better just because you leave your partner, that's guaranteed. No therapist would endorse this.
I know it sounds harsh. But I've known many fellow OCD sufferers in my time and tbh, when we're in the thick of things, we can desperately reach for something to stop the anxiety and it can fall into controlling behaviour. It comes from wanting to control our space completely - an impossible and isolating goal - but if you give in to this and leave your partner, then it will just move onto other things you or others do. Such as: don't drive that route, don't make noises in the house, don't hang out with that person, don't buy this, don't use this.
What she can't see right now is that OCD evolves and finds new ways to trigger the anxiety and thus continues a cycle of obsessional thoughts, physical or mental compulsions, desperate attempts to "cure" by extreme controlling of the environment. I'm fortunate that mine tends not to gravitate towards actually controlling other ppl specifically but I'm aware I'm still a handful in other ways when I'm unwell.
OCD UK and OCD Action both have the support for family and friends. They will advise you not to enable her by giving into such demands. It doesn't help. What DOES work: ERP (exposure response prevention therapy. The above charities will tell you both more about it. Trust me when I tell you, if you give up your partner you will begin a cycle where she'll rely on others completely to help her cope, but she needs to learn to do this for herself, and ERP, support groups and self help tools will empower her to do this. It's a work in progress, for her and for you as family.
If your family once again tell you to end your relationship to fix this, tell them what I've said, from someone very involved in the OCD community who has NEVER seen someone get better by putting the responsibility for recovery on others. She's 20, an adult, and has to take ownership of her recovery. When she gets better, she will be grateful you didn't enable her, because the momentary relief would simply be replaced by a new compulsion/obsession. It's the nature of the beast unfortunately. But recovery and learning to handle it IS possible and there's real support to help her do it.
It is a terrible illness, but you are not alone x