Well, if you could find a way to fasten the paper towel to the bottom, that would keep her out. Tape can be dangerous if your leo can get to it, but here's the setup I use.
I have an UTH, which is a little too hot for the tank. Rather than spending money on a thermostat, I layed down a piece of (free from the grocery store) corrugated cardboard that is cut to almost exactly fit the tank. I wrap it in paper towel and set it into the tank. With the paper towel wrapped around it, there's no where to hide.
When cleaning day comes around, I can lift the cardboard out and easily wrap it in paper towel. You can tape the PT around the backside if you need to, but it usually isn't necessary.
I don't know if this would work for you with your setup, but you can probably find some lighter cereal boxboard that will work just as well and won't significantly inhibit the heat (if that's a concern).
-----
Blaine
0.0.1 HY/Patternless/Normal Leo (Echo)