Would it help to bring your own supplies? Often times artists will wear smocks, can you get a few to wear while working at school? It sounds like a tough situation. Can you talk to your counselor again and maybe tell her more of your thoughts behind your concerns? I know I sometimes have trouble making clear my needs, and needed to write it down so I can get it all across. I tend to freeze up and not be able to explain myself if there is a misunderstanding or if the person doesn't get what I'm asking. A lot of times for me, what I ask ends up sounding like something total different than what I'm trying to ask, so I get a lot of negative reactions. When that happens, I have to do myself and correct what I am trying to say by telling the person that I don't know how exactly to ask, but that I know it's coming of wrong. It sounds like that happened with the counselor. I don't know how helpful that would be with the library situation, but maybe you can ask for a conversation to brainstorm ideas on how to handle the ocd in the library? I sometimes also am not sure what to ask for when asking for help. If your solution is not acceptable to the university, would you be open to taking to them about what is difficult about the solution? It might be helpful to pull your private treaters into this at least by having conversions with them. . It doesn't sound like the counselor at school is getting the magnitude and value of your concerns. Maybe you can practice what you want to say with someone else first (either your boyfriend or your pdoc?).
Also, you said you are on meds, can you something extra for the anxiety before heading to the library or art class? It may not take it all away, but it could take the edge off.
Just some thoughts. It sounds like a tough situation. But congrats on coming so far already.