I have been selected for an interview with a different department in the same building. Is there any way to keep my current supervisor from finding out about it? I'm fairly certain she'll make my current job even more of a hell if she finds out, and especially if I don't get the job and have to stay put a while longer. HR does not announce interview schedules so someone would either need to leak it to her or she would need to ask HR directly. Any advice?
This is tricky. In a lot of companies, she'd be almost guaranteed to find out. (In fact, in a lot of companies, policy would require that she be told.) And hearing from someone other than you that you're interviewing for other jobs in the same company is likely to go over less well than hearing it from you.
If you're really desperate to keep it from her, I'd say that you should mention to HR that you're concerned about a bad reaction from her if she finds out and ask for their assistance in keeping it confidential for now. Ask them point-blank if that's something they can do.
But prepare for the possibility that it may leak out regardless. Be ready with an explanation that will control any fall-out from her as best as you can -- it's an opportunity you can't resist, you love the company and love the idea of your career progression not taking you away from it (and by extension, also love her), blah blah blah.
On the other hand, maybe her reaction won't be what you fear. I've noticed people tend to be far, far more nervous about telling their boss they're leaving or thinking of leaving than they actually need to be. Unless your boss is crazy or totally unprofessional (both of which are possibilities, of course), she should handle the news like a grown-up.
Let us know how it goes!