Not sure about pop-ins. I still change sam once in the night, but he is still in the same nappy on a good night for upto 8 hours. i have used slinki minkis - well stuffed with WN trifold and my onesize BB with same insert with no problems. The minki is huge but doesn't leak! The other pockets i trust for a long period are- WN OS, FUNKY NAPPIES (but these are generous fitting) and a starbunz (this is lower rise on sam but v reliable if well stuffed.)
I find the WN sized nappies small compared to others and although i have not got a fleece pocket i would think that might be good and may not swamp her. I have also got a little kiwi quick fit which works well at night (not a pocket- i know).
Not sure what you have tried- may have tried some of these, but hope that helps!