Which kinda carseat? Do I buy booster?

Star is a chick Answered:
Boosters are never appropriate for children under 4. Putting a child in a booster puts them in charge of their own safety in the car. Until a child will remain seated properly for the entire trip, a booster is a dangerous choice. Most children are not ready to handle the responsibility of a booster until age 5 or 6. Here is a visual of how the belt needs to fit when a booster is used http://www.iihs.org/research/topics/boos if the seat belt is moved out of place before a crash, the injuries can be fatal.

Evenflo Maestro, 18" top slots, 50 pound harness limit, outgrown in booster mode at the same time as harness, high back booster only.
Evenflo Securekid 300/ 400, 18" tops slots, 65 pound harness limit, no info on booster fit, will be released in the next few months
Graco Nautilus, 18" top slots, 65 pound harness limit, makes a good booster, converts to high back and backless booster
Graco Argos- same as Nautilus but harnessed to 70 pounds and has a no-rethread harness (don't need to uninstall to adjust height)
Britax Frontier, 20" top slots, harnesses to 85 pounds, converts to high back booster only, tallest harnessed seat and booster on the US market

Your daughter has outgrown her current seat if any of these occur
1) She reaches the harnessed weight limit of the seat
2) Her shoulders are above the top harness slot
3) The top of her ears are above the shell of the car seat

If she has outgrown the seat you currently have, she cannot ride in it again- not even once. Get a new seat immediately. If she still fits in her current seat, you have some time to purchase a new seat.

snwflk1109 Answered:
You need a booster seat with a harness on it… if money is tight, the Evenflo Maestro (around $60-$80) will keep her harnessed until 50 lbs and/or her ears are even with the top of the shell. If you have a bit to spend the Graco Nautilus (around $100-$150) has a 65 lb harness and the headrest will adjust to accommodate a taller child (the Maestro is quite a bit shorter and doesn't adjust). Then there's the Britax Frontier 85 with an 85 lb harness… however, it's more like $250-ish.