Ok, if she isn't eating this is what you need to do:

Go to the store and buy some baby food. Not mixed vegetables or anything with potatoes, carrot will work. If you have any Vitamin C powder, mix a VERY little amount in with the food. Feed her through a syruinge (sp?) WITHOUT the needle. If she won't take it, force her to eat it.

Since she is over a year, she shouldn't be eating any alfalfa. Get her on timothy hay! Alfalfa has way to much nutrients for her!

How long have you had her for?

Get her to a small animal vet or a vet experienced with guinea pigs. If she won't eat the carrots, try offering her a little bit of apple.

Does she have any signs of being sick other than not eating and drinking? (Crusty eyes, nose, etc.)

Also, force her to drink.

If you can't get baby food mash up 1 banana or boiled carrots with a little water and feed it to her. But don't give her too much banana, it will give her a tummy ache!

If you need any more help just PM me. I went through the same thing with my guinea pig not too long ago (he is ok). Just please get her to a vet soon!