I like it lower, but it isn't unsafe where it is. If it were up higher, it wouldn't be safe. Brinlee fits in it similarly, and it is safe. I wouldn't have allowed her to ride like that if it weren't safe. I even had it checked out by CPSTs, who also agreed it was indeed safe.
I actually think it fits slightly better (lower) on your DD than mine. Mine doesn't use this as a booster anymore, she's in a Britax Parkway SGL.
The Graco Turbobooster is also a great choice.