We put a gate on DD's bedroom door when she started getting out of the bed, also did rapid return too at about the same age. Sometimes she would fall asleep on the floor and we then moved her back to bed. (usually after tantruming)
DD went into her bed at 18 months, at first she didn't realise she could get out the bed, which was great, then the terrible 2's started at around 20 months. She was definately able to understand what was going on. I'm sure she'll be fine.