What's the ambient temp in the room, and the temp on the heat pad/cool ends inside the tank?
If the room is quite cool the end farthest from the heat pad will collect quite a bit of condensation. And if the gradient from hot to cold is too sharp because of the colder room temp, and the hot spot is too hot she'll sit in the colder area most of the time.
At least this is what I encountered when moving my animals into the basement. Your mileage may vary.
One thing you could try is putting layers between the pad and the enclosure. Just increase the thickness of the layer over the length of the pad area so smooth out the gradient, and give them more choice on where to rest.
I'm *not* an expert though, this is just what I've been working out on my own.
Good luck