Do not limit her hay intake; hay is the most important part of a chinchilla's diet. I actually limit the amount of pellets (my chins get only a small amount of pellets; I fill in a small treat cup with 50% pellets & 50% herbal supplement) to make sure they eat lots of hay. Herbivores thrive on good hay and herbs; just look at a 2000 pounds bison. It's important to offer a diet that closely resembles the composition of the foods that chinchillas consume in the wild. Many captive animals suffer from diseases that wild animals do not suffer from or they are not common in wild animals. Many domestic chins suffer from dental problems because people decided to change their diet, and offer pellets instead of various grasses and herbs. Chins are born to slice through coarse vegetation with front teeth and their back teeth are designed to break up grass by grinding action. Pellets are just crushed between teeth – crashing action does not wear down molars properly and fast enough. As a result, they can become misaligned and can cause the misalignment of the incisors as well. Another possible problem is the development of sharp spurs when the back teeth do not wear each other down any more. Pellets also aggravate the condition in chins with teeth problems. It's not only about tooth wear; teeth also grow faster on high energy diets.
Unfortunately, many pet owners think that chins need a bagged, "complete" diet as they have been conditioned by manufactures who claim that they know what we should feed our animals. As a result, pet owners think that a bagged diet is better than a natural diet and afraid to follow the logic. Surprisingly, we do not think that a pelleted diet that consists of about 4 ingredients and lots of synthetic nutrients is good for us or for our children.
Here is the truth about animal nutrition. Feeds have been developed by trial and error as we lacked detailed knowledge about diets of wild animals. The scientific study of diet is young, and it's not an exact science; new substances are being discovered all the time. Pelleted feeds lack enzymes and important elements, including secondary compounds that possess medicinal properties (in the wild, nutritional = medicinal). A pelleted diet can not replace a natural diet and goodness that Mother Nature offers.
I'm happy to see that more and more vets recommend to reduce the amount of pellets chins get and offer more hay. They also explain the importance of coarse stalks.