I second the advice to provide a land section, possibly by filling an appropriately-sized tub with dirt or sand and placing a rock or other type of "ramp" adjacent to the land area. A basking area alone is not sufficient for a female. I made the mistake of housing my female spiny in a large aquarium without a nesting area since I had acquired her before she reached maturity and never exposed her to a male during her 14 years in my care. She apparently developed eggs anyway and died after a retained egg ruptured and caused an infection. Your turtle may just drop all of her eggs in the water without complications, but I will not take the risk now that I know about it. One trick I learned from the Spotted Turtle forum was to place a thin (1/2" to 1" layer of sand on top of the top soil so that I would be able to tell when the turtle had dug a nest hole.