She does look pregnant. But you've got a potential problem even bigger than a normal pregnancy. Pregnancy and delivery are very hard on guinea pig sows, not least because the pups are huge in relation to the size of the mom.
But guinea pigs carry the genes for some defects, and your pig may well be a carrier. Roan (your pig is one) or dalmatian pigs carry genes which cause lethal white pups. They're all white, born blind with small or missing eyes, deaf, with wonky and/or missing teeth, and immature digestive tracts. If they survive, they require lifelong expensive vet care, including frequent tooth trimmings.
They're just one of the reasons why one should never buy a guinea pig from a pet store. The breeders that supply them often know nothing about guinea pig genetics, and care even less. A reputable rescue will not adopt out a pregnant roan pig, or a lethal white pup unless the potential adopter knows exactly what they're getting into.