Why was Kelly resistant to starting estrogen therapy which would eliminate estrogen from her body?

Kelly was disturbed when her doctor told her she must begin estrogen therapy; that is, eliminate it from her system as a precaution against "growing" more cancer. She'd have to wait for more children for at least five years. But she'd be 42 by then, she reminded the doctor. He responded that she did have two beautiful daughters. She was angry but finally Edward was the voice of reason and told her that he and the girls needed her.