Fortunately for you, guinea-pig babies are born at an advanced stage. When the babies are born, the mother will produce milk in her breasts. Sometimes, however, the milk will not be released and will make her become sore. This is due to hormones. Usually persistent suckling will bring this to an end but sometimes the mother is in pain and will become more and more irritable, driving her babies away. If they manage to suckle, this stimulates the missing hormone which will allow the milk through.

From your letter, it would seem that this was the case. I certainly would recommend that your pet can have another litter next year since this is not a behavioral problem. However, I would advise against any female pet giving birth to a litter every year.