Cardew older cousin? Lizzy's branch are MCHB, but her family are the broke end - so she could be UC or MC HB and biracial. Her parents are white but 'Letitia's' mother needn't have been.

She could be one of Natsuko's muggle born English aunts - UCMB, her family also has a history of expecting women to enter miserable 'good on paper' marriages'.

Valenduris granddaughter or great granddaughter - from one of his daughters from his first or second marriage - which could make her potentially HB and/or not white

Greyback sister - UCHB. some played sibs, morally grey family. Could also be a non-white cousin of the current branch