One thing you could do is share with her the stories of people who have OCD, e.g. videos on YouTube or even posts on this forum. Perhaps she never thought that people's lives could be flipped upside down by OCD.
I don't think it's worth sharing the details of your personal struggle with someone thay has a baseline level of ignorance about the topic. I think it would instead be wise to tell her politely "Hey btw, comments like 'Im so OCD' are a little insensitive because they mischarecterizing a very serious and debiltating illness" see how they take that. That'll be a good gage as to whether you should open up about having it at all.
Yeah, that is hard to deal with. My mom is willfully ignorant about OCD. I didn't want to tell her, but she caught me at a weak moment. She also told me that I never tell her anything and also shut her out. I didn't go into much detail. Her response was "I think everyone is a little OCD" it triggered a massive spiral and I almost quit treatment. A good rule of thumb is something a friend who also struggles with her mental health, but not OCD. First rule of mental health Learn to differentiate who deserves an explanation, who deserves one answer, and who deserves absolutely nothing. It sounds like your aunt is someone who deserves nothing. Don't feel guilty about that.
"Learn to differentiate between who deserves an explanation, who deserves one answer, and who deserves nothing" I love this! What a good mindset when living with any mental health issue in general. You don't owe anyone an explanation by default.