Well as someone in the 'Puter biz I understand. No one thinks until something breaks.
okay well I would explain to your supervisor that this kilt is Mary's problem not yours. You are wearing a garment steeped in history and tradition of your cultural heritage. It isn't offending anyone (I am assuming you wear it well, and don't misbehave in it) and that indeed you tried speaking to her about it but she didn't take you up on it. You have done what you can, you have been and will continue to do your job. You are also at an advantage being not only in California but also at a University. Remind your supervisor that many of the Alumni are proud Scots and Irish, and that your being rebuffed because of being proud of your heritage isn't something to be taken lightly. Or something along those lines.
This is about her, not you. You need to be fair and explain to your boss that you tried to work it out but she wasn't having it. And also however indirectly let them know you're feeling "pressured" and a little "Hostility" in your work place. These two words are key for HARASSMENT, which can lead to big suits.
I am not saying go on the attack but be prepared to fight for yourself, don't just rollover on this. She has a problem with you, and that happens but that is no reason to make you be the only one to deal with it. People clash, but BOTH people have to be adults and get past. It's part of a job. You tried she didn't.

Sorry so long in response but this gets me a little heated.