I'm very fuzzy headed but i'll try to type up a reply.
First of all congratulations on managing to hold down a job, that is worth a note and is something to be proud of
It can be difficult trying to manage an illness whilst at the same time being employed by people who know nothing of it. There's always the fear of discrimination, and worrying about how you're coming off to others. It's entirely up to you whether you wish to disclose your illness, it depends on your relationship with your bosses and managers I guess.
If the person doesn't know about schizophrenia or how it can really affect people chances are she was just thinking that you were deliberately being lazy or bending the rules with regards to uniform. I wouldn't jump to any conclusions, and sometimes some people are just neat freaks when it comes to looking at other people.
Perhaps you could ask you family whether they think you look neat enough when in doubt before going to work? Chances are if they think you look fine, then the person was just being silly. It's entirely up to you though whether you wish to disclose your illness, maybe write to your manager that the staff member is causing problems for you and explain in the letter about why you didn't disclose the illness at first but that you'd like it taken into consideration.
Anyway, don't let one idiot at work get you down. You're doing very well maintaining a job as well as the scoring 100% on the mystery shopper thing.