Hello, I'm a 31 year old woman who had very severe OCD from 17 years old.
I completed my last year of sixth form partly at home, I then dropped out of uni at 20 because of how severe it was. I find OCD quite a hard thing to explain because it really is quite broad. For me, in hindsight, I had OCD 'traits' in childhood (very perfectionist, worrier, not tolerant of uncertainty). It then just kind of grew and by the time I was 20 I too, like your daughter, wasn't leaving the house or getting out of bed etc. I do find OCD & depression go very hand in hand. It's almost like a seesaw, when the OCD has been too high and exhausting for so long, the depression swings in to give a break from it!
In terms of recovery, my parents in the end paid for private therapy sessions once a week. It was CBT ERP (exposure response prevention). They paid because the waitlist was so long, but if you're nearly at the point of seeing a psychologist that sounds good! Sometimes I find the NHS isn't great for not giving the length of time needed if people are quite severe, so it may be worth considering if you can 'top up' at the end with private. I received PIP which paid for the sessions, I would certainly recommend your daughter receives disability benefits as the horrible truth is you do often have to pay for private mental health help.
ERP for me was incredible, it absolutely helped tons with my OCD. I also have a family friend whose daughter had a similar struggle & was put in touch with me, she also recovered really well after ERP. I think I was a particularly complex case, mostly because of how severe the underlying perfectionism was in me plus I have a bit of a mood type disorder, so I do still receive PIP now and have my weekly therapist which allows me to now live a great life working, seeing friends, and not finding life a constant struggle!
I also know the Maudsley Centre in the UK is exceptional for OCD and you can get NHS referrals, we tried to push this through my local MP at one point. And the book 'Overcoming OCD' by David Veale & Rob Wilson is the gold standard self-help plus has a great bit for families and loved ones.
The good thing about OCD is that it really can get better. I think of it as a kind of maladaptive coping mechanism to uncertainty & eventually you can begin to sit with uncertainty and tolerate it more with the help of those therapies. It's particularly intense and cruel when you're in it, but thankfully absolutely can be treated.
It's been a huge part of my life & I'd be very happy to discuss anything else with you if it helps. Welcome to ask anything! I do want to say too that I definitely have a few linked mental health issues so I'm not the typical case still needing therapy in my 30s - and my therapy isn't for OCD at all, it's a bit more general and helping me work through big identity issues. Everyone I know with OCD really did recover so well after say a year or so of ERP!
P.S. Sorry, writing this off my phone so it's jumbled but I just remembered your concern about causing it. Please do not blame yourself, OCD is most likely a chemical thing or arises in sensitive people. It's absolutely not something to crucify yourself over. I have the most wonderful parents & have had such difficult struggles, if anything it's only caused our relationship to be stronger. You clearly care so much for your daughter, so try to be nice to yourself too. It's not your fault!