OOOOO , what a cutie !!
I have a guinea pig too , Jasper !
Can your sweetie (what's the name ??) drink and eat on her own already ?? In a pet store , you could buy a baby-pet-bottle and a kind of milkpowder which needs to be solved in water . I would make a paste of normal guinea pig food and put this in her mouth bit by bit . A bit fresh salad is good too . Good luck !!

ps. This afternoon , I can ask my sister-in-law ! she is an expert in raising guinea pigs ! I will post more then !