A.W.
how old is your dd? how much does she weight? if you are concerned about it not being safe enough its b/c its not, boosters just arent as safe. you should really consider getting her a car seat with a higher weight harness (HWH). here is a crash test video showing the difference b/c a 5 pt car seat (passenger side) vs. a booster with just a lap belt (drivers side). there are seats that can keep your child harnessed till 65lbs and also to 80 lbs. this summer there are suposed to be 3 more HWH seats comming out. you have to keep in mind that each change in a car seat (rear facing(RF) to forward facing(FF), 5 pt to booster w/lap belt) is not a "milestone" that you want to get to, its actually a downgrade in safety. if you want more info you can email me or you can also go to car-safety.org and read through the forums (and ask questions) to learn more about car seat safety. my DS is 23 months and 27# and 36 in and he is still RF and will continue to RF till he hits 35# (the RF limit on his seat) and then when he outgrows the seat at 40# he will most likely be getting Britax Regent which will 5pt harness till 80 lbs http://www.britaxusa.net/products/detail_regent.aspx
i hope this helps