The comment about baby-wipe containers caught my eye. They sure do love them, but if they are the ones where you tug out one at a time through the “star-shaped” hole in the lid, then maybe give it a miss, they shove a little finger in, and then try and pull it back out again. No fun for anyone.
My son was a horrible sleeper when we were somewhere other than home. Not sure there is any way around it. It sounds like you came up with a good plan. It should get easier as she comes to learn “how” to sleep at your place.
She’s a lucky baby to have you. Your sister is also extremely fortunate.