|My 28-lb 2-year-old is able to use both the L Sandys and the One Size as pull-ups. Or, more accurately, I can pull them up and down on him, as he has zero interest (I'm trying to teach him how to pull up underwear and this is a real challenge). Those both need a separate cover, though, so I guess part of the question is how important is it for you that she be able to manipulate the diaper by herself? If crucial, then you probably do want to stick with something that's one-piece (in my case, at present that wouldn't make a bit of difference, alas). I haven't used the All-in-one diapers, but wonder if something like that might work for you. They aren't designed to be pull-on, but depending how the sizing/weights work, a size slightly larger than she'd truly need might work for that?