Catherine Sanderson was one of the earliest known Demons of human origin. It is thus very fitting that she was part of the first wave of new demons to separate from the Domain of Law, following the collapse of Aether after the Omen. Her involvement in the creation of Pandemonium, alongside Nathaniel, is perhaps her greatest legacy, though of course it was not an easy path to get there.
Her troubled family life, in particular tensions with her sister Gabriela, are well documented. It is believed the two were very close, but found them on opposite sides of the battle between Celestials and Gaians, with Catherine's sister joining TERRA around the same time as it is believed Catherine ascended to demon-hood.
The exact alignment of these events is hard to know for sure; whether it was Catherine's transition that pushed her sister into TERRA, or the other way around, we'll perhaps never know. It is known that Catherine had had strong ties to Demons before this period, but it is not clear how much Gabriela knew of this.
However there is no doubt that these events cause a divide in their relationship, and following Catherine's move to Pandemonium, it's not clear that the two were ever reunited. Her focus instead remained on her new-found family of Celestials, and worked to ensure their protection thereafter.
— From A Brief History Of Pandemonium by Amelia Dixon, published 2185
The scene opens on the figure of a demon, accessorised in all of the excitement that modern prosthetics can provide and lying on a bed. Their hands are dark and twitch creepily every so often. Beside him kneels a woman in a tight dress with tiny horns.
'It's no use Catherine, my one true love, my darling. I can't fight it much longer… the Nyx… it taints me…'
The woman stands up, a determined expression on her face.
'Then I'll fight it for you.'
— From Meet me in Havering Hill, a romantic film