ocd is an axiety driven disorder. people with ocd tend to have a lot of fear of something, and tend to have their thoughts accentuated towards negativity.
its this same negativity that can make people develop a bad and evil opinion of Allah especially if they misinterpret the following hadith:
there's a hadith qudsi about how Allah will not like those people who did actions for fame/show, actions that were not for his sake. i don't have the exact hadith on me, but the point is that people with ocd may misinterpret this hadith
and unfortunately disregard Allah's mercy and hence develop a bad opinion of Allah.
they need to remember to do their best, and have hope in Allah's mercy that they did their best to purify their intentions free of insincerity. essentially, ocd people (who by the way are fairly intelligent) will do so so much to purify their intentions, they might go into despair, from the
excessive ocd fear and not have a balanced opinion of fear/hope in Allah's mercy.
also....as for ghusl....ghusl "every hair on the body must be wet" - while its true that you need everything on your body to be wet for ghusl, ocd people may take this literally and go to extremes, thereby taking long times in the shower. the key thing is not whether you actuually wet every hair on the body, but whether you
think you got everything wet. having said that, it's extremely difficult and unrealistic to wet every millimeter of your body. Allah just wants you to do your best. when its said"every hair on the body must be wet" they're giving a guideline to cover everything, but they're still saying ghusl needs to be easy and not difficult.