IMO if she's still happy rear facing and is within the height and weight limits, no need to rush turning her around :-). Some kids actually prefer rear facing b/c they can rest their feet/legs on the back of the vehicle seat instead of having them dangling in front of them forward facing - you can see photos here http://www.cpsafety.com/articles/RFAlbum.aspx .
My twin DDs were rear facing up through 2 years and 8 months until one of them hit the rear-facing weight limit of their seats (which was only 30 lbs. - these were seats made in 2002).
Edited to add: and it may seem counterintuitive, but CPSTs have found that a child's legs are NOT endangered by remaining rear facing if their legs can touch the back seat - please see the following from http://www.cpsafety.com/articles/stayrearfacing.aspx:
"Won't my child be uncomfortable? Where do his legs go?
Many parents have the misconception that children are uncomfortable or at risk for leg injury by having their legs up on the vehicle seat or bent when kept rear-facing. These concepts are completely incorrect. First, children are more flexible than adults so what we perceive as uncomfortable is not for children. Think about how your child sits in everyday play. Do they sit with their legs straight out in front of them? When they sit on the couch, do they purposely sit so their legs dangle out over the edge? No. In real, everyday life, toddlers and preschoolers CHOSE to sit with their legs folded up - that IS comfort to them.
Second, there is not a single documented case of children's legs, hips, etc. breaking or being injured in a crash due to longer rear-facing. There are plenty of cases of head and neck injury in forward-facing children that could have been prevented if the child had remained rear-facing. However, even if a leg or hip were broken or injured, it can be fixed. A damaged spinal cord (from forward-facing too soon) cannot be repaired and subjects the child to lifelong disability or death."
Good job keeping her RF this long!