"For the sake of our inquiry, let’s settle on a definition of rape."

No. We don't need a definition. We need a connotation. Playing dictionary games is an intellectually dishonest ploy to appropriate the connotation of a forced sex act to apply it to unwanted impregnation. What Daphne did is no different morally from stealing a condom and using a turkey baster. The sex was not forced, only the paternity. Forcibly inserting that act into your definition just harms the word; it does not worsen the offense.