My guinea pig has lost weight....
 

She's gotten very thin and bony, and Im not sure why :(
I'm worried about her, I know she eats, she eats her food, carrots, cucmbers, timothy hay, grass, spinach, celery, and lettuce
She also chatters a lot, I'm not sure why...
Have her teeth grown too long? Does she need to gnaw?

She's about 3 years old, and has a friend who is a few months younger than he and probably weighs about 2x as much- I'm worried about her- Help?? :(