Diarrhea is very serious with chins. Both my chins have had diarrhea in the past. One time it was because I gave him dried fruit, which I never do anymore. Another time, I took them traveling with me and the stress of the car ride gave them diarrhea. Another time, I think it might have been the Mazuri pellets that they were on. Once I switched them over to PANR, they're fine.
If they have diarrhea, they need to be on fluids. Most likely the good bacteria count in their stomach is out of balance. If it's serious, your chin needs to be on Bene-bac and some kind of antibiotic; if not, with Bene-bac itself & time, the diarrhea will run its course.
Diarrhea is serious; considering a chinchilla is not a big animal and can easily lose fluids, and they're good at hiding symptoms that could point to other illnesses, taking your chin to a vet who specializes in exotic animals would be the best idea.
Since you mentioned that your chin is getting better, just keep an eye on her & provide her with lots of hay. No more dried fruits.