You do not assist feed an animal that knows how to eat and that is healthy.
The first thing you do you make husbandry changes (always do that before offering alternative preys), because an animal is in the same setup than other identical animal does not mean that that setup works for that specific animal.
Downsize as much as you can V18 tub (or similar foot print) or 12 quarts tub or similar foot print, provide aspen or coco coir chips as bedding, wait a week and offer food. I would also recommend to lower the temps and not go higher then 86/88 on the warm side and 78 - 80 on the cool side.
This is a new one on me and one I have never tried. Why the lower temps?