I have a very timid dd11 as well (Barnstormer scared the pants off of her, and now she hates it, for example), and she just LOVES Soarin' --thought you could pass that along to your dd. This past Jan. when my dh, dd and I went to WDW, we just didn't ride the "scary" rides. Frankly, I'm the only one in my family who enjoys them, so it really wasn't a big issue.
Do I think it's safe to leave your dd while you and dh ride a ride? Yes. Would I have felt comfortable doing that? Probably not. Really, only you can judge your comfort level, but I do feel it would be safe.
Have a great trip!