My singer is a pain in the arse

So basically we’ve got a gig in a couple of days and at the rehearsal last night she just started playing random songs. Me and our bassist have had enough of this and we’re stressing about this gig but she’s not putting in the effort. Also she’s been writing this song for 3 weeks and has only wrote the one verse for it and is demanding we play it at the gig. Anyone got any advice