Family usually have some kind of relationship between their Enneagram numbers. Because Matthew is a Five, Marilla’s Enneagram will either be in the strength-weakness number relationship, or in a Head Type adjacent number.
A Five in strength moves to Eight, and an Eight in weakness moves to Five. These siblings have a great dynamic, a great partnership even, because Marilla is an Eight.
No matter how genteel Marilla plays it, you know she wants to take Rachel Lynde’s head off sometimes. Very Eight. Her firmness in disciplining Anne is Eight-ish. Pleas for mercy are not effective on an Eight, and they don’t move Marilla. She’s a hard nut to crack, and when I read the novel as a child her character was very unsympathetic to me. Only later did I appreciate her no-nonsense pragmatism.
Marilla enters very reluctantly into a relationship with Anne, but once she’s in she will defend Anne to the death.