It would make sense, but I think that Princess Celestia and Sombra had twins, Sunset Shimmer, and Starlight Glimmer. I mean, just look at there photos.
They look a lot alike, even their pose. They also have a streak through their mane. My theory is that Princess Celestia and Sombra loved each other sense they met, but when Sombra found out that Princess Celestia was going to have a foul he got mad and tried to kill them (Princess Celestia and Starlight Glimmer) later she found out she was going to have twins. while taking care of them she noticed Starlight always picking on Sunset, she knew Starlight was going to be like her father so she banished her to a small town, and marked it on a map. That's why she gave the map to Twilight, so she could make her good again, like how she did with Sunset.