I'm so glad to hear to hear your pet is recovering. If you can it might be a good idea to do a fecal culture. It's possible your chinchilla has some kind of parasitic infection that might flare up again later. If that happens anti-parasitic drugs are recommended.
What I mean by uncontroversial is that it's usual, normal ingredients that I would expect to find in a chinchilla diet. I'm also going to recommend, if you can, ordering some oxbow critical care and just try that and see if your pet will eat it. It will probably take a while to get it shipped in. It's a different recovery diet. Just feed some on a spoon. This kind of diet is better in case of an emergency in the future.
There are many different possible causes for this kind of problem. Anything from bad food, to changes in water (Perhaps you should switch to bottled water), to stress that might cause an underlying parasitic issue to flare up. You may never know what caused it and may never encounter it again.