Your daughter should be able to bend her legs and sit cross legged. Most kids naturally do this. I have a 14 month old and he has no discomfort. You as an adult might think of the position as uncomfortable, but babies/young children are much more flexible and it doesn't bother them.
Lisa hasn't done her research on this. Rearfacing is the absolute safest position and you should keep your children rearfacing up to the rearfacing limit of the seat. Legs can be fixed....spines can't.
http://www.youtube.com/watch?v=psmUWg7QrC8&feature=re...
http://www.car-safety.org/rearface.html
http://www.msnbc.msn.com/id/9916868
http://www.cpsafety.com/articles/StayRearFacing.aspx
http://parenting.ivillage.com/baby/bsafety/0,,9r5v,00.html
http://www.carseat.org/Technical/tech_update.htm#rearfacFF
** just edited to add....I wasn't trying to be snarky or mean I was just stating what I felt to be true. I just think too many parents rely on what their ped says (and yes while they are educated doctors they aren't always the most informed in some areas. Their specialty is disease and health issues) or word of mouth instead of researching the latest updates to things like this that have a huge impact on the safety and well being of our kids.