yeah I think the ambiguity is in the last sentence. I mean if you willfully continue to penetrate her after she said to stop, then yes it is rape. If she says stop while you're doing it and you take a few more pumps while slowing down and coming to a stop, that is more of a blurry area.
Either way I think a girl has the right to say stop if she decides she isn't comfortable with the situation, even if it is during the event in question.