When could your toddler climb into their car seat on their own, especially if it was rear facing?

Lately c (2) has been trying to but for now it's just easier and faster to do it myself. I'm starting to realize I might need to start letting her and giving her the practice, as I get more pregnant and then, you know, have a newborn. We currently plan to keep her RF until right before the baby is born, since she doesn't complain about it. (Obviously I will still buckle and tighten the straps, though she insists on doing the chest clip first). We have a mid size SUV and she has climbed into the seat once when dh was putting her in and we weren't paying close attention. Whoops.