My daughter is 11 weeks old. At 3 weeks, she was having some difficulties that would cause her to vomit a couple times a day. The pediatrician recommended keeping her elevated while she sleeps, and to let her have time flat on her back while she's awake. I got a rock and play and keep her next to my bed. The vomiting has since stopped, and she is sleeping longer stretches at night. I don't feed comfortable keeping her asleep in the rock and play for up to 8 hours while she sleeps. However, now she now associates laying flat on her back with play time, so when I lay her in the crib, she thinks it's time to play. How can I get her to sleep in her crib again?