It has nothing to do with "needing a good stiff one", but rather needing an affirmation that the night together meant as much to him as it did to her. Her initial negative reaction to his shock and confusion was her own embarassment and frustration that the romantic spark that she felt for him and that she'd thought they had just consumated was not in fact reciprocated. She was throwing him out because of how difficult it would be to live with someone she had unrequited feelings for who had rejected her.
When Chameleon-as-Peter showed the sober intimacy with her that actual-Peter had not, she read into it what she wanted to read into it and decided to forgive and forget Peter's initial reaction, writing it off as not being fully awake, lingering alcohol, whatever. Once it's settled in her mind that he does reciprocate her feelings, she establishes that they are now in a proper relationship, thus further sex is a-okay, as well as her efforts seen here to turn him into a suitable boyfriend. A verbal heart-to-heart that ended with "Peter" confessing feelings for her would have had the same effect.
Of course, there's still no excuse whatsoever for playing for laughs Chameleon-as-Peter raping her. At all. Ever.
Also I'll grant that even if the above was the intended reasoning, it still wouldn't be great storytelling (though at least not completely offensive), and the fact that the writing -could- be taken as "hot dickings = compliant woman" would still be failtastic.
And he still absolutely no matter what needs to tell her that it was Chameleon. Not doing so goes beyond dishonest and into "accessory after the fact".