Have you sat them down and talked this through with them? In a constructive way of course as yelling only makes people defensive. Because partying so hard your voice suffers is bad. It should be a wake up call, not 'oh, lets skip a few songs then'. Less partying (as in no party at all) is in order, so she can spend the time developing new routines and learning new songs. Because routines, just like songs, need to be fresh. That's why bands learn to play new songs and put old songs to pasture. And it sounds like the other guitarist REALLY wants to be in that Kiss tribute band. He should really make a choice, either stick with the Kiss tribute band, or understand this is a different gig that requires no one person Kiss medleys. Unless its on the setlist of course. Although in theory it does sound like something he could do as part of a routine while you change/tune guitars.
If you have talked this through with them, in a constructive way, then maybe you should start to think is this the band for me? If yes, then accept that this will be the way things stay until it hits them in the face. If not then look for something else and leave. Or stay in the band while you do something else and make that your main project, while this becomes something you do on the slide for extra $$$$.