There is a trick to get one of your favourite girls to dance on stage and you need to watch them perform (from a distance of course) in order to unlock their dances, also i believe that fexa is the only one who can’t dance for some reason however i don’t know if the devs change that in the 2.3 and 2.4 update i will need to investigate this.
Oh if you need help getting the girls to dance on stage look up mastermax888 YouTube channel he will show you how to get the girls to dance on stage.