Leena Sullivan (Christina and Charlotte's mother).
Pureblood, ambitious, shrewd, cunning, leader, and achievement-oriented, Leena has most of the qualities of the Slytherin house, but she grew up in a muggle-friendly family and thus she isn't convinced of the superiority of wizards with pure blood, instead she finds muggles fascinating.
She's 18 years old in 1981, when Harry Potter saves the wizarding world, those where hard times and Leena had to hide with her family more then once because as you know, Voldemort used to recruit pureblood wizard and witches.
At the age of 19, she was able to leave the wizarding world and finally live in the muggle one, where she shares a flat with her friend Gena, a muggle born witch who attended Hogwarts with her but was sorted into Hufflepuff.
Together they started to go to College and eventually they both graduated; there Leena met a muggle, Carl (Carlyle) Bierce, a young welsh man who worked in a office near the College.
They started dating and had a relatioship of six years before getting married in 1989, in 1990 Christina is born and two years later, in 1992, Charlotte joins the family.
Leena stayed at home until Christina turned 8 and then started teaching in a muggle school, she is still a teacher but now, after divorcing Carl, Leena and her daughters are living in Hampstead, in the same house that was their shelter during the second wizarding war, from 1996 to 1997.
I did it again, hope you like the new one (: