First double-check the temperature on the hot side. Are you measuring the temperature on the tub and not the paper over the heat pad? If it's not pushed hard/flat against the tub, even a tiny air gap between the paper and the tub can cause a huge difference. So, your tub may be too warm.
Second, is your tub in a rack now, or is it just sitting out in the open? Even with the hides, you may need to cover the sides and/or top with a light towel to make her feel more secure.
Third, your girl may have just hit the "1000 gram wall".