question for OT medical experts

She might have to undergo a certain amount of chemo/radiation, certain diet, preparations, etc.

Most types of cancers won't change much in less than a month.

Not an expert by any means, but I've had two. First was a few days after finding it and the second was a bit more complex so there was a week or so wait.

There are a lot of variables that go into that timeframe including the type of cancer, stage as well as prior chemo/radiation, so in answer to your question...it depends

Depends. Some cancer surgeries involve multiple specialties needing an 18 hour slot in the OR which is not easy to get. Plus competing with other surgeries already scheduled. Usually things don't change in 3 weeks.