the front row is supposed to be nearly 40' off.
If you look down, you're up there!
However, my older son who hates heights rode this ride 4x and loved it! If your niece is young enough, she cans sit cross-legged, that may help her to not feel as if she's up so high.
Also, the screen pretty much grabs your attention. I didn't look down until our 3rd time on the ride!