Guinea pig hair loss?

guinea pigs don't have hairloss when they are old, so yes id say its mites. my guinea pig had mites and he lost his furr and the other guinea pig he lives with constantly didn't show signs of mites besides scratching, the only thing i could think of it would being is a fungus or mites, it would be really uncomfortable for your guinea pig so you should do something to treat it, don't say its not worth taking to the vet because it is, all they need to do is give you medication and it works, or you can go to the petshop and they will give you some over the counter stuff for mites, use it and your guinea pig will be happy and her hair will grow back.. also, my guinea pig who was loosing his furr from mites also got mad and bit but he never did before, so shes probably biting because shes in pain and shes irratated, get her some treatment, if not thats really cruel. for the meantime you could bathe her and brush her hair.