Back in the day, Katerina was a young woman wearing Victorian clothing. She had darkly colored hair, and wore a long dress and a bow tie.
In the past she appeared as a loving and smiling mother. She seems to be a nice vigorous lady.
At some point she met the Earl of Millennium and became close enough with him to cry when he 'disappeared'.
Then the Earl turned into two infants, she adopted the both of them, named them Mana and Nea, and she raised them as her own children in the Campbell Residence.
When Mana became ill she watched over him day and night until he eventually recovered.
At some point, an a bit older Katerina was badly wounded by the Earl of Millennium. The Earl then announced to Mana D. Campbell that everything was back to what it used to be. But it is implied that Katerina survived.
Searching for A.W arc Edit
Katerina has only appeared in some flashbacks, but not as a person yet. She is mentioned by Nea in front of the earl .Meanwhile in Nea's inner world, Cross Marian (or an illusion of him) tells Allen to go to the Campbell Residence and to find Katerina. 
- Katerina doesn't have the "D" in her name that both her adoptive son have. The "D" could come from their father or from something else peculiar about them.