How old is she? DS has climbed out twice when not feeling well, but has not made it a habit. I would do as pp suggested tonight and put some padding down and see if she does it again. If it scared her when she bumped her face she make think twice about doing it again.
IMO, if she is not at least 2 1/2 - 3 yrs, and she keeps climbing out, I would opt for the crib tent. We moved our first at 2 b/c she climbed out, and spent the next 6 months getting up 2-3 times a night putting her back. Or just sleeping on the floor next to her.
The bed rails keep them from falling out, but not from getting out of a bed.
You can order the crib tents from First Step Ahead web site. Just google it.