Has this happend to you

So my baby is around 8 MO she now moves around she moves upwards when shes laying down she will use her little legs to push herself up so Ived noticed now when she sleeps in her crib she will move upwards as well so sometimes in the middle of the night I'll find her waking up because she's all the way in top of the crib like her head will hit the bars of the crib because she pushes herself up. So my question is what can i do to her crib so she wont hit her head since i don't keep nothing around her crib cause of safety.