Hi Claire -
Well, I bet you it is the "almost crawling" that is causing the night wakings. This is a big developmental milestone and I have read tons of posts from moms whose babies have nightwakings due to rolling, crawling, standing, etc. I have not had this experience myself yet as my dd is slow to do most things!
The only other thing I can think of is maybe she is ready to drop her catnap?
When she wakes up in the middle of the night what does she do? Does she cry? If she is not crying and does not need you, just leave her. I know it is hard to do as you know you could just go in there and get her back to sleep quickly but going to her could start to cause a problem. I have had experience with this with my dd waking early and I just laid in bed listening to her chat to herself until it was our normal get up time. This approach worked but it sure was annoying to listen to her! The key is to be consistent with how you deal with the nightwakings. If you are consistent, she will learn.
I hope this helps a bit and I hope you get some sleep soon!