Yeah, even when they're YOUR characters, they still sometimes refuse to do what you want them to. It's a shame you can't knock them over the head to make them behave.

(The second story I sold to Circlet, although it ended up falling out of the book so I suppose its mine again, had one character who refused categorically to sleep with her ex-girlfriend. I finally got her to agree to bitter angry sex, because it had to be an erotic story and she had no interest in cooperating)