When then, if she believe he is on the "verge of death" will she not allow you to take steps (buy a smaller cage) to correct the situation to help him begin eating again? This baffles me.
A tub is very inexpensive. They are usually less than $10. Even so, if you wish to keep him in that tank, I would add as many hides as you can, fill the tank with fake plants or balled up newspaper to make him feel more secure and then leave him alone for a week or so. Then try feeding again. Don't make a ton of changes and then attempt to feed the next day.