I have tried them all for Amy and I find all mine love the big corner box. It is low enough for Amy to get in, big enough to move around in to dig and high enough for them to stand, sit or do whatever. Amy's legs can not hold her when she squats so all her business has to be done standing and she has PLENTY of standing room in there. It is tall, long from front to back and side to side. Also you may want to try a storage container, one at least as tall as she is, cut a end to make a place to get in and out and cut low enough so she don't have any problem getting in and out.