She is born at Nyköping Castle and and was named after her grandmother Lady Märta Finvidsdotter.She is the only child of Nils Jönsson Oxenstierna born in wedlock to survive infancy. Her mother was Nil's third wife Lady Karin of Gumsehuvud- Sture. When Felicia was six years and eight months old, her father was assassinated. Two years later, her mother died from a mysterious sickness, probably poison. She fled to Holywell with a servant name Harold Magnusson, where she was adopted by her uncle, General Varana of Westmorland, and his wife, Lady Giovanna.