In "Food for the Common Cold," what are David's mother's and David's grandmother's opposing opinions about telling Frick about the hysterectomy?

David's mother does not want to tell him, because she is afraid that once he knows she cannot have more children, he will leave her. David's grandmother thinks this might be true, but she says that David's mother has to tell him, regardless. She also thinks it might not be such a bad thing if he leaves, because in her opinion he is no longer a good man for her daughter.