Any Advice?

My dear little girl has finally learned to sit herself up. Yay! One problem with that is she no longer rolls over and goes to sleep when I put her in her crib. Well, she does and then fifteen minutes later when I'm checking on her she standing up in her crib whispering at the wall. Yes, whispering. I'm pretty sure the little stinker knows she's supposed to be sleeping but would much rather play. At first she didn't realize that after she sat up she could stand up so I would find her asleep like this. Notice her foot up by her head. The other one was the same on the other side but her blanket is covering it.

Now she stands up too and it's a lot easier for her to keep herselp awake when she's standing. So, to those of you mothers who may have run into this problem, is there anything I can do to get her to go to sleep? (As of now I rock her to sleep but I don't want to have to do that everytime.)