I believe you are referring to the I-94 website, not the ESTA one... that (digital) form is the legal limit of her admission so she cannot be accused of overstaying if she follows that.
That said... they obviously have all sorts of classified places to put notes that you can't request, and there was clearly something in her file that made them suspicious in the first place, so staying the full three months is almost certainly not going to improve that.
That said... they obviously have all sorts of classified places to put notes that you can't request, and there was clearly something in her file that made them suspicious in the first place, so staying the full three months is almost certainly not going to improve that.