I had the long legs issue with ds (still withing the weight/ height limit) but they find a way to make themselves comfortable and honestly if it came down to it id prefer 2 broken legs to a broken neck.
Yay for you.

When you have seen the youtube clips of long legged children rear facing in European countries, you won't think your DD looks squashed at all. If she isn't at the height marker yet, keep using it!