It sounds like that therapist said something that your W did not like and that is why she's ready to find another one. If "he" told her she should find a different therapist, then they may have had a falling out with each other (lol). Hard to believe he would be willing to just let her go. Anyway, I'm glad b/c maybe a new one will help get her on the right track.
I'm thinking that if she's willing to see a MC then that is a good move if it isn't just to confirm she should move on and do whatever to be happy. Be sure you ask the C if he/she is pro-marriage b/c if not, then that C will not try to help with the M and will agree with divorcing.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
