How can I stop a doctor from performing surgery on my daughter scheduled this Monday?

My ex-wife scheduled the surgery behind my back. I was not told of the doctor consultation. We have 50/50 co- parenting custody. She is violating our decree. I simply want the surgery postponed until I have opportunity to consult the surgeon and a doctor of my choice for a second opinion. As a caveat, the surgery is invasive but not an emergency. Thanks