I see you now have all the info on the laws, wieght limits, etc. but while you are shopping for a booster, keep in mind that a 5 point harness booster is the safest for children. I have both the britax frontier AND a safeguard go (which is now safety 1st go hybrid booster).
The safeguard go is the safest booster on the market and it converts from a five point harness, to a high back seatbelt booster, and then you can eventually remove the back and just use the seat booster part. I know it is a little on the pricier side, but you won't ever need to replace this seat.
See the article http://www.safeguardseat.com/media/documents/news/safeGua...
Do your research when it's time. I watched so many crash videos and it didn't take long to convince me that my child's life has no price tag.
After you've done that, go to a store that carries the brands that you are considering and comparing, take the floor samples out to your car and install them. The one that fits the best and installs perfectly is the one for you. Bring your daughter with you, because she must fit in it and be comfortable in it too. (you aren't obligated to buy it there either as with most seats you can find a better deal online).
This is the reason I have both the Frontier AND the Safeguard Go. The Safeguard Go fits better in my primary vehicle, and the Frontier fits better in Dad's truck.
I posted a while back a much larger response with links in it to car seat safety stuff so feel free to see my history of responses. It is 'Booster Seat' and it has a lot of other advice on boosters - good reading.
Good luck!