Hi,
I would say give her another 2 weeks to settle in offering food once per week. Assuming she doesn't start losing a lot of weight she should be fine.
Every change you make to her enclosure (such as changing substrate) may be enough to unsettle some snakes so leaving it a little longer might be the best course.
Does she have any nice dark hides in the tub? You might also try bumping up the hot end temps slightly if the extra settling in period doesn't help.
Just my 2c.
dr del