Just wondering how anyone else would feel in this situation...

Before I got pregnant I worked full time. My manager always spoke of the future and said she would like me to become a supervisor of our department and move up. Just as I fell pregnant a new person started in our department below me. I trained her fully in her role and then also in my role to cover holidays. It was then decided this new person would be covering my role while I was on maternity. We become quite good friends and she opened up to me about her worry over taking my role then what happens when I return, I told her in confidence I wouldn’t be returning full time but would hope to return part time so she would be fine. Fast forward to getting closer to my return to work. About 2 weeks ago I was chatting to this person who is covering my role about my possible return, opened up about me being unsure if I even want to return and that my current manager had mentioned a part time role but I wouldn’t consider it due to the days etc. Now I’ve just had a call from my manager and that person saying the person covering covering my role is now my supervisor and will be dealing with me going forward and my return...unsure how I feel knowing the previous conversations we’ve had as friends and the fact that I trained her less than a year ago in both roles she’s done in the company..