It says she waited until she was 40. For any medical school graduate, it would be a sign of unusual ignorance not to be well aware that most women’s fertility has substantially declined by that age, and that not a few are completely infertile by that age. For a surgeon who has specialized in breast surgery, in other words whose practice consists largely of women of middle to late child-bearing age for whom the possible effects of chemotherapy on future fertility prospects would be a common concern (with the question of how likely it was that they even still had any fertility to warrant trying to protect, being an important factor in patient counseling, with life-and-death implications), it’s not even remotely plausible, unless she was so clueless and incompetent that she should have had her medical license yanked decades ago.
She’s not a random “educated and otherwise-aware woman”. She’s someone whose profession of three decades has required her to counsel patients as they make difficult decisions about treatment options, including the decision as to whether to pursue or forego chemotherapy as part of a treatment program, while weighing the likelihood that it would make a difference in whether the cancer recurred or spread, against the likelihood that it would bring fertility to an end. If she wasn’t knowledgeable enough about the normal fertility curve to counsel women who were 39 or 40 that foregoing chemotherapy to protect fertility likely amounted to risking cancer recurrence in an effort to keep something they’d already lost anyway, she had no business practicing in this area of medicine.
She "hadn't realized"? --- as you yourself pointed out, the possibility of that being something other than a rhetorical hyperbole is vanishingly remote. I think it's possible you're taking one throw-away line which gives far from a complete picture, and using it as an excuse for expansive derogatory speculation.