Who is Maisie Maidan from The Good Soldier and what is their importance?

Maisie Maidan is a twenty-three-years-old, newly married, and having an affair with Edward Ashburnham. She suffers from a fatal heart defect, and travels to Nauheim for treatment in the company of Leonora and Edward. At Nauheim, in a moment of frustration, Leonora boxes Maisie's ears. Afterward, Maisie decides to return to her husband, but she dies from heart failure as she is packing to leave.