You could try moving the lay box. If you have it at the warm end, try moving it to the cool end or the middle temp zone and vice versa. If it's not at her preferred temp then she might keep looking for an alternative.
What substrate are you using inside the lay box? Perhaps she'd prefer something else. Vermiculite or sphagnum moss are the usual ones - if given a choice, mine prefer the moss.
How damp is the substrate? Could it be too wet or too dry?
Sometimes they can be picky over where the entry hole in the box is. I do have a couple that express a preference for having the hole in the lid rather than the side (yes, I know, I do spoil them...).
There are a number of variables about the lay box that could be causing her to not settle. However, I usually find that no matter what, they will eventually realise that it's the best place to lay - even if it isn't their idea of the perfect place to lay. You can either try and figure out what's causing the problem, or just sit back and wait.