Her name is Agatha. She was named this because her mother told her all she did was cause agony in her life.
Aggi got home late, so she became invisible as she walked in. She did not know her parents could see her. They told her she could turn invisible since she was a kid. They thought it was funny. Aggi knew nothing else. They had kept her isolated. She was their experiment to see what they could get away with. It was purely for their own entertainment.