'young miss Griffith'

Age range 11–21 | MCHB | any house | either student, debutante, or pursuing a passion | suggested pb is Saoirse Ronan

This young girl/woman is connected to Samuel Griffith by way of being his niece. Her father is his older brother Gilbert Griffith, who regrettably has done a rather poor job with that. Samuel now intends to adopt her. Will she accept?

I left the age range open to your preference. Important to me is that they will have a relationship that centers on the themes of family and belonging, for better or worse. Much of everything else is up to you.

Young Miss Griffith grew up in London in a townhouse where she lived with her parents. Gilbert and Isabella Griffith (née Dunbar) are unhappily married and provided not much of a home life to her. Isabella is frequently taken by nervous breakdowns, and Gilbert is a weak and fanciful man who works as an assistant healer at St. Mungo's and suffers from addictive behaviors, the worst of which are gambling and abusing sleeping potions. The girl spends a lot of time between places, often with relatives like her grandmother, who is a Muggle.

Samuel Griffith, for the earlier part of her life, depending on her age, is absent. He has fled from being cajoled into providing for his entire family instead of following his passions and is busy in Europe, becoming a great Alchemist.
When he returns, he drops in and out of the family landscape without really communicating much about his plans and thoughts. What he does is start shoveling galleons into the furnace that is the family estate. He starts settling debts, and materially, things improve a lot.
When he is present, he is a stabilizing figure for the girl, but he has the habit of dropping off the face of the earth without warning.

Recently, he has taken up his position at Hogwarts. This is connected to his decisions to no longer enable his brother's gambling habit and to shut Gilbert out of the estate.
To not harm his niece's prospects in life, he extended an offer to take her in and provide for her, formally adopting her.
The specifics of this arrangement depend on her age.

That is the starting point. Everything else, we can plot together!