To my mind, Elizabeth Valerian is the one of the more unique characters in the House Valerius series.
She is the daughter of Lukas & Sara Valerian and grew up in Shadowcroft Manor alongside her cousin, Ash. Due to this, and the similarity in their ages (Elizabeth is roughly six months older); the two of them are almost as close as siblings, something which is reflected in the way they talk to each other (or so I hope).
However, as they’ve become older there has been some friction between the two of them. Part of this is the result of a childhood accident referred to in House Valerius, where Elizabeth is confronted with the reality of Ash’s; and by extension the rest of the family’s, need for blood.
The other reason is that Elizabeth is most prominant member of the Valerian family (in the main series anyway) who does not carry the Ceteri mutation. As a result, not only is she something of an outsider among the rest of her family, but she will age at a normal rate and will die before they have aged more than two or three years. A Life Almost Ordinary, set during her early twenties will explore this aspect of their relationship.
By the time of the events in House Valerius, Elizabeth has mostly come to terms with her position in the family and acts as one of the main legal counsels for their businesses. She continues this role in A House Divided while also becoming something of a facilitator for Ash and his companions, providing them with information, money and other necessities as the plot takes them out of the UK.