Another thing to keep in mind when handling this is,
DOCUMENT EVERYTHING!!!
If you e-mail "Mary", cc your supervisor.
If you speak to her, or she speaks to you, write it down, verbatum. then show your notes to your supervisor.

Don't just "keep the boss in the loop". Get him involved. Tell him, "I've offered to talk to 'Mary', she refused. Tell me what to do next"
Get your supervisor to do the talking to Mary. Get your supervisor to talk to her supervisor.

If, as you believe, your kilt is the only reason Mary is being the way she is, then you are the agrieved one here. The pressure and influance she is putting on your expression of your ethnic and cultural heritage IS WRONG! Reverse the role, IT'S STILL WRONG!

The important thing is get your boss ACTIVELY on your side. Do nothing towards Mary. That's his job.
It is also his job to approach and forward your case to the 'chain of command' and the appropriate Human Rights Office at your University. That office is more used to handling Womens cases of harrasment but you have the right to have them involved here too.

Get this out into the open, light of day. Do not sit and stew over it. In todays world there is no place for this behaviour.