Does it wake the others up? As long as she is willing to stay on the mat then yes she should stay there the whole time. Naptime isn't always about sleeping but of resting and giving the body a chance for relaxing. If you can put that child closest to the door and maybe after the 1 1/2 hours you could get her up and put her in the kitchen but maybe in a highchair so there is no chance of her running back into the playroom and then give her something quiet like playdough. Is there a chance that she is one of your last arrivals in the morning in the sense that she is getting more sleep before coming than the others are. The older she gets the more you will be able to make her understand laying quietly. While she is sleeping can you slip a couple books or something near her for her to use quietly on her bed.