i think if she is that tall then yeah go for it, i have a go safe booster i think its called i got it from baby kingdom.. bout 2 yrs ago now.. and i used it early due to my ds height also..
i think its safer to use a booster if she is out growing her seat but you can also get the ones that have the same belts as the baby seat itms?
then one i have has the full belts not a harness and i love it its great its exactly like a seat and its comfy too.. also has the side protectors so if any impact comes his head is cushioned..
im not sure if that brand is the one i have i havent really looke din a while but if your interested i can find out..