In German sources, she is referred to as filia Regis Sweonum ("daughter of the Swedish King").
In 1961, Danish genealogist Sixten Otto Brenner interpreted this to mean she was the daughter of King Erik Eriksson of Sweden.
However, Hans Gillingstam challenged this conclusion, arguing that it is more likely she was the daughter of Birger Jarl, the regent of Sweden.
[1] In the same sources, Birger Jarl's other daughter, Rikissa, is referred to with the same title.
[2] According to some sources, Catherine may instead have belonged to the family of Counts of Gleichen, which had connections to Danish royal house.