Marianne (Mary) Walker married the 10th Phantom. Lee Falk had the 10th marry a Scandinavian ships daughter. Marianne makes more sense and has appeared in more stories and is accepted lore as the 10th's wife.
She had an older sister, Beth and older brother Will who were criminals and shipwreck plunderers who both perished at sea as they tried to escape. Her mum was an opera singer from France and dad was a Scottish nobleman, who joined Rob Roy and lost his arm in one of the battles.
Mary suffered a lot when the 10th Phantom was wounded, lost his arm and had to retire from the Phantom.
Nothing on her death.