Depending on what her dose
of the xanax was before the surgery, if her current dose
is way lower, she might be in a state of withdrawal.
I don't know a lot about benzo addiction, but do know that a lot of folks suggest switching to valium to taper, since it has a much longer half life, it stays in the body longer, avoiding the rapid crash that comes from xanax leaving the body much faster.
I think the family doc who said it is impossible that she is addicted to the xanax is full of ****.