While I agree he shouldn't do anything to her while she's drunk, the easy way to resolve that is to take her to a hotel so she can shower and sober up...if she's still wanting to have sex 1-2 hours after drinking, then she's obviously not under the influence anymore, specifically in her case since she only had a sip of 1 drink.
Now if she was shit faced then yeah just straight up avoid that altogether, since it would take quite a few hours for her to sober up.
Escorting her back home is definitely the safer move though, and I think a lot of girls might appreciate you not taking advantage of them