Yes, no sex of guinea pig is better than another. Your guinea pig is a sow, sow bondings are successful 80% of the time. Do you live near an animal shelter that carries pigs? If so, I would recommend adopting, there are plenty of cute little pigs in need of homes, If they carry multiple sows, take miss Rosie into the shelter. Some offer bonding services, they would pair your pig up with multiple sows and observe how they get along. If the two don't get along, then they try another sow. And you also mentioned how can you tell if a pig is lonely, do you observe the pig in the hut a lot? That can be a sign pf loneliness.