Sleep, I need Sleep!

I know I knew what I was in for before I had my 4th child, but it is not her stopping my sleep. DD#3 has never had problems sleeping, she was sleeping through the night at 5 weeks old. She has always gone down for her naps and her bedtime when it is time, but for four days now she has rebelled. Tonight she learned how to get out of her crib. I put the video camera in there to watch her, and sure enough she is slipping over the side. Lil Houdini is what DH is calling her. She hurt herself though, so what do I do. Do I just keep putting her back to bed and hoping she won't hurt herself too badly, or do I let her roam the house as I drowse off on the couch. I think I am going to have to get her a toddler bed, but then she won't go to sleep when she is supposed to or she will wake her baby sister while crying. I am just so warn down this week. I just put her down in her bed, and she finally fell asleep without knocking on her bedroom door. I just don't know what to do. I am guessing atleast with a toddler bed I could leave her in her room and she could get back into her own bed. I don't have the strength to deal with another rebeller, I thought I had atleast a break with her since she always went to sleep so nicely. Atleast DD#4 is getting really close to sleeping through the night now.
She is completely out, I better get myself into bed then. Get my sleep while I can. Wish me luck!