Marion Trelawney Walker
Phantom Wiki URL
Lee Falk says she is American but no mention of her name. Team Fantomen has her English with her father an English Lord. A good compromise is that her father is English and her mother American.
In the first story, it isn't mentioned how her and the 12th Phantom married or anything about their marriage.
Marion is a real balancing act for the 12th Phantom. She is the reasonable one, the quiet steady influence and a little skeptic which has rubbed off on her son, the 13th.
Marion is the daughter of a Lord and likes nice things, balls, gowns etc.
Nothing on her death has been explored.