Or maybe she'd make you a medium long?
I have a lot of trouble with our DnFs falling down in the back (hello, bum!
). The medium seems to stay up better than the large (odd as the rise is shorter), but I have to fasten both of them much more tightly around the middle than I would with our other nappies to stop them sliding down in the back.
Then I worry about them being uncomfortable for Lili (like wearing too-tight jeans