Behavior Changes After Gastric Bypass

One of my best friends for over 20 years got the procedure 6 years ago. I was always loyal and supportive to her no matter what she weighed. I was a size 6 most of my life as she struggled upward of 200 lbs. Ever since she got the procedure she has acted differently toward me. She has become distant and aloof. She seems like she has low grade depression. I am hurt that this operation has changed her into a person I don't really recognize. The sparky glow she used to have is gone and she doesn't seem to want to engage with me accept at certain events when I am back in town. I moved far away years before her procedure. Nothing happened that I can point to that would cause this dramatic change in our relationship. She seems like she is confronted with being friends with me or not. I love her dearly. She was my Maid of Honor. Can anyone fill me in on the reasons for changes in friendships post surgery?