What should I do about my stressed guinea pig?

I rescued two abandoned female guinea pigs. One guinea pig is doing fine, but the other bigger one seems very stressed. She wouldn't eat and would not come out of her house. I gave her to another lady who lives by me and has a lot of animals, my guinea pig is still doing fine, but after reading a lot of info online I am wondering if I should get another friend for my pig, or if I should go get the other guinea pig back, in case the separation is stressing her out more. My friend said the other guinea pig still won't eat and still won't come out of the house and this has been going on for over a week. HELP!!!