- And got the T-shirt
She didn't survive the labor. If you'd realized earlier that she was having problems, an emergency spay might have saved her.
The death rate for sows and pups is high, which is just one of the reasons we NEVER recommend that you breed a guinea pig. There are other reasons, including a number of genetic problems that can result in deformities and lifelong pain.
She may have had one large pup that was too big to go through the birth canal. Or, if she was an older pig, her pelvic ligaments may have been to stiff to separate to allow the birth. There's no way to know, unless you want to take her to a vet for a necropsy (that's an autopsy). If you do, refrigerate (don't freeze) her body, and take her in tomorrow.
Please do NOT get another female to go with your male. There are thousands of unwanted guinea pigs in rescues and shelters, and there are enough accidental pregnancies to keep the species going. There's no need to ever deliberately breed another guinea pig.