What would you have had this person do? Leave their child unattended? Do you have children? Who takes care of them if you have to work late?
Irrelevant, the nature of your reason to refuse to work outside of scheduled hours is between you and your conscience. Be it a child, a dog, opera tickets, or Friday Night Magic - the rules have to be the same. Being a parent doesn't absolve you of responsibilities to patients nor does not being a parent increase your obligations to work additional hours.
Her disinterest in finding someone to cover is disappointing in a healthcare professional - but otherwise "I can't stay late tonight" is fine unless contractually you are on call.
This is potentially a reasonable point. If the surgeon can't make a compelling case to the on-call anesthetist that the case needs to be done, then the anesthetist present has a reasonable argument. That said, I've found that day shift staff may well stay late to handle a case they had already prepped for if that would prevent an up-prepped on-call from having to come in an hour later.
One of my parents is a physician and I didn't get to see them much when I was growing up (or even now); I intimately understand the point of view of those advocating for greater work-life balance in medicine. What I find lacking in the push for greater work-life balance is an acknowledgment that quality of care may be changing for the worse as a result.