The old sphynx-cat Mallory has known Archie since he was a baby and has had a soft spot for him ever since. She is a no-nonsense businesswoman, but also a true people person. 

When Archie returns to London, she tries to guide him away from danger, but her advice falls on deaf ears.

For Reference:

The character is similar to Professor McGonagall

The voice is more like Meryl Streep (Example of her role in Doubt, Example of her role in The Devil Wears Prada)

Ca. 5 lines

In this scene she barges through Archie's door, who's packing his stuff, about to leave to join his father's former gang. Mallory is angry, she cares for Archie and this is the last thing she wants him to do. Her anger is like that of a worried mother.