I have 4 guinea pigs. Since yours is over a year old that's too old to have babies (ideal pregnancy age is around 7 months), likely will cause complications, and there would be a lot of trouble following even if the mother and the babies are ok. For example, need to get separate cages for the boys and girls after 4 weeks...
Guinea pigs do eat a lot...pellets, timothy hay, various veggies should make up their daily diet. Limit her pellets if you don't want her to get too fat, but hay and veggies shouldn't be limited.