Can she get in and out of water container? I can't tell from the picture. If you're not sure, put her in and she if she can climb out.
I'd recommend some chicken wire or something over the top to keep out predators. Having lost a turtle years ago from lack of a protective cover, it's better safe than sorry.
Other than that, looks nice to me.
Does it receive any direct sunlight? My concern would be a kind of greenhouse effect through the tub.
Good point on drainage.