Hi Shannon, Sounds like you have a little thrill-seeker like my 7 year old girl. :)
Space Mountain is an exciting roller coaster. The minimum height requirement for it is 44 inches, so to avoid disappointment be sure she measures up ahead of time. Don't worry, there aren't any flips, loops or corkscrews on this ride. There are several big "dips", but that's it. In fact, the highest speed Space Mountain reaches is 28 miles per hour, it just feels much faster in the dark. My daughter rode it with her hands in the air, and begged to go right back on it :)
If your daughter is at least 44 inches, she will also be able to ride Expedition Everest at Disney's Animal Kingdom Park. After 3 times in a row, I had to pry my little girl away from it.
For more information on Space Mountain, click:
HERE
Hope this helps and that you have a Magical Vacation!
Kaylene