In a series of side missions under Orphans Escaping, the mission briefs give the player an idea of the life a typical Shinra orphan led. The orphans are placed under Shinra's “care” facility in which Shinra claims is built for the orphans' protection (orphans are brought from various locations throughout the world). In actuality, the orphans are forced to undergo harsh training and are set to be assigned to various battalions that correspond to their skills/talents and the training they received.
According to the Keywords Collection from the Crisis Core: Final Fantasy 7 - the Complete Guide in Cruise Story & Visual Archive, Cissnei is from the same orphanage as the escapees, suggesting that she would have received the same harsh training that made some of these children decide to escape from the orphanage.7
Shortly after Cissnei introduced herself to Zack, she encountered a more advance Genesis Copy that was giving her some trouble. After Zack rescued her and defeated their enemy, the Genesis Copy tried to escape by flying away on its one wing before Zack struck it down again. Upon seeing the Genesis Copy's wings, Cissnei told Zack of her childhood dream of having wings:
Cissnei: When I was a kid, I always wanted to have wings.
Cissnei: You know, like an angel.
Zack: If people had wings, they'd be monsters.
Cissnei: Wings symbolize freedom for those who have none.
Cissnei: They don't symbolize monsters.
Although the purpose of Cissnei's little speech was to cheer Zack up or give him a different perspective, I think that having to endure the type of brutal training that makes Shinra orphans want to escape in present day, Cissnei was longing to have a normal childhood or perhaps, although we do not know at what age she was brought to the Shinra orphanage, the days that she used to live before being raised by Shinra.