I have a kokatat Idol (not to be confused with the Icon). In a packraft she probably won't have any issues with the butt zip being uncomfortable. I had a Meridian for a while when I was just a Packrafter and the chest zipper was terrible but it was the older metal zipper. The newer plastic zippers are flatter and will probably be more comfortable whether they're located across the chest, the back, or the butt. After I started kayaking I realized that the older metal butt zipper was awful in my kayak as it hit me right on the hip, but once again not a big deal in a packraft since everything is squishy! I ended up with the 2 piece Idol as my second suit for everything and I love the versatility.
The Idol is easier to pee out of (it comes all the way apart at the waist!) but a little more difficult to zip back up when wearing a spray skirt and rescue PFD. I figured out that if you don't unzip it all the way then it's better. It ends up being cheaper because you dont have to buy a separate dry top or dry pants- also great for international travel and long trips like the Grand Canyon.