How much does she weight?
DD1 was off the charts for height as a toddler and 75th for weight. She was still able to rear face to 2.5 years in the classic Britax Marathon.
DD2 is 90th for height and weight and still rear facing in a First Years True Fit and SK Radian. The True Fit has a rfing weight limit of 35 lbs, so we'll hit that before she turns 3, but it's a great choice for tall thin kids.
I'm planning to buy the Graco My Size 70 (same seat as the Graco Size4Me) when BRU has their trade in event. I know they are having harness issues with their seats, but from what I've heard, Graco is working on a solution (and offering pretty good customer service). This seat rear faces to 40 lbs and has an adjustable head rest that can rear face in any position. According to that, DD1 would have been able to rear face until 4 years, and DD2 should get close to 4 years rfing also.
I have no experience with the ProRide itself, but we've been very happy with our Recaro high back boosters. I would think that the ProRide should get you rfing to 2 years and probably ffing to 4 years. I think it kind of depends on what you want to do with the seat.