How can I stop my guinea-pig being so lonely?

I had a rabbit once that lived with a guniea pig. My rabbit treated the guniea pig like its own baby so when she died the guniea pig was left alone and acted similary to yours. I bought her 2 baby guniea pigs who were the same colour as my rabbit and from then on she came out to play etc. She looked after the baby guniea pigs and loved there company. For that reason i think you should buy another couple of guniea pigs either very young or the same age as her.