EDIT: oops I just reread your post. Good luck on taking out all that gravel!
You could raise the water level. Turtles love lots of water to swim in. They're natural swimmers, so don't be afraid of making it higher. But add water in gradually so she can build up those swimming muscles!
You shouldn't feed bananas too often since they're high in potassium which isn't too good for your turtle.
Do you have a UVB basking light?
Have you read over the care sections on this site?
Good luck with your turtle!
Kevin
oh and, welcome to the forum!:D

2 Chinese Goldenthread turtles ~ Miso&Mafan
1 Chinese Box turtle ~ Chief Lemon
2 Redfoot Tortoises ~ Sheegua & Muugua
1 Toy Poodle ~ Pudding
3 firebellied newts ~ Cassandra, Mr.Poo, and Wiggles.
http://flickr.com/photos/the_naturalist