OMGoodness surgery? Poor girl. So glad you (and the vet) found the problem. That is amazing 30 stones plus gravel in that little tiny bladder. No wonder she was in pain. I'm glad she is doing fine and I'm sending lots of positive thoughts that she will have a speedy recovery. ((hugs)) to both of you.
I'm sure Molly will have a healthy, happy life with you as her mom.