K.W.
The recommendation is to keep them rear-facing until 2yo. It has nothing to do with height or weight and everything to do with the necks in her muscles being able to support her head in a crash. Google "internal decapitation."
My dd was tall for her age and her legs were definitely tucked in. But she stayed backward until 2yo.
The recommendation changed at some point after 2009. My first daughter (born in 2007) was rear-facing only until she was 1yo.