I'm so glad to hear Milli's surgery is over and she's on the road to recovery. She will adjust to her cast, don't worry...it might take a day or two but they do figure it out. Meantime do try to keep her confined and quiet because it will help her heal. She may need a slightly bigger crate though, or maybe an indoor x-pen that you can put a bed and her toys in but still keep her quiet.
I wouldn't worry about using puppy pads at this point...you do what you have to so she's comfortable and that might be the easiest way to keep the crate clean until she can manage to stand.
Good luck and please keep us posted!