It's about a foot high already but I can do that. I think she clumsy because she tries to do what I ask.
Is she hitting it with the front or back? If she is just dragging her feet, it might help to have a series of poles, not just one, to exercise and get her to stretch and lift for a few strides at a time.
Woah - let me back up... a foot high? It might just be too tall for her to walk over easily. She's a pretty low kneed, low hocked horse isn't she? She might not be that limber if she's not used to that kind of thing. I'd lower it to poles on or near the ground, and work on her gymnastic ability with more poles, not higher ones. You'll want to work out the spacing so they are just one footstep between them. If you ever really come upon a log that big on trail, she'll figure out how to clamber over it. :~D