I recommend the Britax models that go to 60+ pounds..there are a few to choose from. You can also often find them at online stores with a discount or coupon, just make sure they are a certified Britax seller so that you know you are getting waranteed and first rate stuff! My 3 yr old is in the Marathon and sleeps everytime she rides in the car with no problem.
She is also REAR facing....at only 26 pounds, it is still the safest. Although the law is 20 pounds and 1 year, it is recommended that they stay rear facing until at least 35 pounds. A professional car seat installer (and firefighter) told me that the inuries to the head, neck and spine that result from a child forward facing are so much more significant and life-threatening as compared to a possible broken leg/ankle etc... Sure, my kids would rather be forward facing, seeing the views etc..but I don't just let them because they would rather do it!....heck, they would rather climb free in the car eating ice-cream and Twinkies too but I don't allow that either :-)
Best of luck finding a great car seat for your little one and hurry and get her out of that booster!
Does anyone know the exact FL law on age/weight for booster use?