My chin, who is almost three, gets a tablespoonful of Pellets a day, and I just make sure there is fresh hay in her cage all the time. Also make sure to take out the old after a day.
NOW...
You said you got your food at the pet store... What brand is it exactly? You need a good quality brand, like Mazuri (Which is the brand I use) to feed her with. Store bought food is often stale and past date by the time you get it, and therefore no longer has any nutrients. There is no benefit to the Chin there.
www.chinworld.com sells good chin food for a good price. Shipping can be a bit steep if you're like me and go crazy and buy a bunch of stuff, but not TOO terrible.
IF you need to change her food, you need to do it slowly. When I got pixel from the pound (yes the pound...) I had to switch her food. It had banana chips and I don't even know what else in it, and that's no good. Do 3/4 what you were feeding her mixed with 1/4 what you're going to be feeding her for a week and a half, then do it half and half, then do it with 3/4 of the new food, and finally, after a week and a half or so of that, you can give her all the new food. This is to avoid upset stomachs, diarrhea, and constipation.
I'm sure other people will have more advice for you.
Good luck!!
