another fan of the bamboozle stretch here
My alternative suggestion is to try weehugger wraps or Flip wraps with your existing prefolds as they are designed for a pad style insert. both companies sell their own inserts but I have used prefold cotton inserts folded into a pad with both of these wraps and it works fine. That would avoid the nippa problem of them sliding down her hips.
There are always flip covers coming up on the boards and occasionally weehuggers. You would need size 2 of the weehuggers. Flip is BTP.