Hmmm... I don't know. What you could try:

I dont know if you've seen them or not, but Target has some "college" shelves that are fairly easy to assemble (obviously, for college students). They come in all different shapes and sizes. You could purchase one of these that would fit in the tub (they have taller ones that aren't as long, and longer ones that aren't as tall) and just assemble the bottom shelf. It would give her something nice to hide under. The run fairly cheap, too.

Horizontal shelves
Vertical Shelves

Or just get a nice long sterlite and melt or cut a hole in it.