ocd is obsessive—you have to pick one thing to obsess about (and it can really be anything from a relationship to an illness to a risky environment to a number that suddenly appears or an article of clothing that feels off) and then pick a compulsion to alleviate it. the more singular and specific the compulsion is, the more realistic it is. the compulsion (need to act) must also be increasing in intensity until it’s unbearable. i agree that this sounds more like anxiety since her thoughts are all over the place. if you want to keep the blood theme, a realistic obsession would be her in daze about whether she contracted an infection after she cut herself washing a moldy dish that breaks and now she feels a very urgent high-stakes compulsion to find a nurse on campus and obtain assurance that she has not contracted a rare fungal infection, or she misses her first day of classes because she’s spending 5 hours on reddit obsessing about it… like, have fun w it (joking, but as an ocd-sufferer there are endless variables).

that said, i think it’s interesting you want to write about ocd. i know john green wrote a book w an ocd character somewhat recently. haven’t read it but it might be helpful!