Yeah that's very small for her age and your vet... (well I would fine another one if/when times come)

If you have not already downsize her to a 10 gallons or 12 quarts tub, leave her alone for a week and offer food.

She could be one of those rare picky feeders that only eat when they fee like it but it could be husbandry related so you want to rule this out if it persist.

Temps nothing hotter than 88 on the warm side and use a substrate like Aspen or coco chips.