Btw, what seat is she riding in now?
If she is FF then I would look at the Graco Nautilis, it too retails for about $180. It harnesses to 65# then becomes a high back booster then a no-back booster, so chances are it will be the last seat that you will need for her. I have been buying Britax for 10+ years (my oldest dd is almost 12) and while Britax seats are great they are not my favorite. I own 2 Marathons, 2 Radians, a Nautilis and an Evenflo Triumph Advance. Imo, hands down, I like my Radians SO much better than my Britax seats. And fwiw, my 4 y.o. likes his Nautilis better than the Britax Marathon too.
If you want a Britax than you can look at the Britax Frontier and the Britax Regent. The Regent is a FF only harness seat where as the Frontier converts from a harness seat to a booster seat. The Britax seats will be more costly than the Graco Nautilis.
Jump over to the car seat board. http://messageboards.ivillage.com/iv-ppcarseats. You probably don't have to post anything since, chances are someone will have already posted a similar question.
Good luck and let me know what you get.