She could have aborted it and made life simpler for everybody. She could have had her tubes tied before it became an issue. Harry could have had a vasectomy. Harry could have given up his magic so that being a father to Maggie wasn't an implicit death sentence for everyone involved. Would of, could of, should of. Had either one truly cared this would have never been an issue. That's the Watsonian view.
Now look at the Doylist view. By implication Jim set up a condition where sex, for Susan, was a triggering event that would cause her to lose control and kill her lover. He modeled that after the Black Widow or the Praying Mantis. He's now done this twice with a female character. Consigning both women to what was effectively, enforced chastity. Making them female eunuchs. While old Harry just carries on. This really borders on misogyny. Can you see that I might find it hard to see the character of Susan as abusing Harry by keeping secrets from him?