Your thread reminds me of when I switched from being student to friend with my guidance counselor after graduating high school. It was a difficult transition and I had a lot of the same issues come up. It took a while, but we figured things out and ate still friends nearly 20 years later.
If it helps, have a conversation with her around the changing rolls. If it helps to think of her more as a mentor, then talk about that. It may just mean that the roll changes again over time. While I still call my guidance counselor my "friend", it is more like a mentor-type relationship. We hang out, we keep in contact, but I don't have the same relationship with her as I do other "friends". We sometimes get into deeper stuff, but mostly it's surface conversations and keeping things light. (Though now that I think about it, that's kinda all my friendships, I tend to be very guarded)...
Anyway, I'm rambling. Sorry. I hope you can figure things out with now-friend, ex t. It may just take more time and more figuring things out...