If she regretted it later, should could accuse him of rape and most likely win due to the 'Murrican legal system
While this is TRUE in that if she could prove that this rape took place that he would be sent to jail even though she raped him in this situation. (because he is an abled bodied man and she is an intoxicated woman)
The only reason why "False rape" tends not to be prosecuted is because "rape" is hard to actually prove in court. The only time I've seen a case where I honestly believed the woman in question was false reporting, mostly because her reputation was tarnished and her support basically convinced her it was rape so the accusation was a way to save her, it was recorded by the alleged rapists (and not even hidden) and she was the only one heavily drugged up (though everyone was drugged out)... And EVEN THEN that trial first hit a mistrial and then the defense waiting until the season was right and redone the trail where they were prosecuted. So even if she was telling the truth, which is still possible and likely as well, it took overwhelming evidence.
So as long as there were no cameras in the boy's bathroom he is fine.
So all in all I don't think fake rape accusations are too big a deal. Yes women are given the benefit of the doubt that they could have been raped, but even then they still have to prove it took place and it was non-consensual.
If she regretted it later
I find it has less to do with "regret". She isn't going to go "I shouldn't have done that" and then charged him for rape.
Mind you hitting him for child support IS an actual and realistic consequence that he might not be able to escape from... because GOOD LUCK proving she raped him (and also... being a rape victim I believe doesn't exempt you from child support).
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Now mind you, I always like to look at cases the as if it could be "Guilty" or "Innocent" as how I judge how things are handled.
It is why I hate law shows like Special Victims Unit (or some terrible episodes of Law and Order) because they will go out of their way to harass, trick, or incriminate someone who very well could be innocent using tactics that would work on someone who was innocent. The worst being a case where a woman accused this guy of being a rapist, dragging him semi-willingly on stage to do it (semi-willingly in that she dragged him... but he could have stopped her using force), and they go out of their way to ensure he is in jail at all points AND the woman in question (and another person) posted sites that basically say terrible things about him. Honestly I wanted him to innocent, I knew he wasn't going to because the SVU are psychic, because really it could have been an episode about how the law is supposed to be objective and that the SVU put their own views and prejudices above that and harassed an innocent person who is actually the true victim in all of this.
Mind you I'd have no qualms if the SVU didn't harass the guy and the episode happened as normal (would have been a good episode about how the system can hide/cover rape)... But if they are going to harass him, there better be a point other then our LEGAL POLICE FORCE being vigilantes who are harassing someone because "They believe he did it", something the police shouldn't be doing and yet the episode treats it as the correct action.