Suu always had the power to leave, but never the will. Listening to Oruha's songs made her decide that it was better to be with people than to be locked in a cage alone, even if it means loosing her life.

Being with people can cause both great pain and great joy, and Suu had already learned about the pain. Her own mother had sold her to the Clover project and had greedily drooled over the money. It took Oruha's song for her to realize the joy being with some one could bring.

Once you know of love and happiness, can you be content to never have it for yourself? The wizards knew this which is why it was so dangerous for her to contact Oruha. If she ever loved, she would have to leave eventually.

Suu escaped her cage (although she did it with permission) and she escaped the loneliness of isolation. The high cost of freedom is suffering, but she was finally able to find happiness.