I’m sorry to hear someone you worked so closely with and trusted is trying to take advantage of you. I commend you for being strong and resisting her manipulative attempts to get information. As a supervisor, she’s well aware that your violation of company policy jeopardizes your job as well as hers. There are two ways you can go here. You can continue to keep the thermostat set to cool on your relationship, or you can call her on the inappropriate behavior just as you would anyone else in the office who asked you to divulge confidential information. It’s your call. If you choose to keep your distance, that’s understandable. She’s violated your trust. Can she get it back? If she’s contrite, she may very well be able to.
If you decide to have a conversation, it’s going to be a difficult one. Think 75% preparation, 25% execution. So, think through what to say and how you want to say it. Thoughtful preparation helps you stay focused and minimizes defensiveness on her part. It also increases the likelihood you can salvage the relationship and possibly strengthen your professional and personal bond. When you get it all straight in your head, and you’re ready to talk, ask if she has a few minutes and find a quiet place where you won't be distracted or interrupted.
Your question to me says it quite nicely, so I would pull from that. Let her know how important your relationship is and how valuable her support has been to you and your career. Tell her that after you moved over to HR you felt uncomfortable with her questions about confidential information, and you started distancing yourself. You wanted to talk about it because you felt ignoring it wasn’t the solution. Then, give her a chance to respond. If she agrees she was out of line and apologizes, give her another chance. If she gets pissed off be prepared with an exit statement like “I wish you didn’t feel that way. I had hoped you would want to continue our friendship, but I see that’s not possible. I’ll continue to work with you in a professional manner as I do with everyone in the office. Thanks for your time.” At some point, she may reach out. She may not. Sad to say sweetie, but some people are only in it for what they can get out of it.
I’m happy to see an up and comer like you taking her leadership role seriously, especially when 'grown-ups' (role models and mentors) are behaving badly. Information is power. In your role, you have it, and others want it. Realize that everyone is not as blatantly obvious in their attempts to get it. Always be mindful of that and keep your desk clear of files, your cabinets and office door locked at all times, and your tequila shots to a minimum. Cheers!
--Your Office Mom