I think that if I had immediately reinforced the form as soon as I cut it off of her, it might have held it's shape a little better. But instead, it took me several days to add tape to the inside (I didn't want it to end up too thick again, so I reinforced the inside mostly). I also thought it was still just too weak, so I added paper mache to the outside and the inside. I wanted it good and firm. Then I spray painted the whole thing.
As you look at the side views, you can see that the form slumped a little and became pretty sway-backed. But the size still works and the clothes don't hang too badly on it, so for now it will suffice. With how fast kids grow, I'll have to make a new one next year anyway. Here it is with one of her swimsuits on.