Standing in crib

My daughter just started pulling herself up and standing in her crib this has made naps a huge problem. All she wants to do is stand instead of sleep. Problem is she doesn't know how to sit herself back down yet and she has fallen a few times and started screaming crying. It's making me super nervous that she is going to hurt herself by hitting her head on the crib. Anyone else have this problem and if so what did you do to help. It's hard to get a good night sleep because I'm so scared of her hurting herself while I'm asleep.