In his 1876 commentary on the Annales Lubecenses, Claes Annerstedt speculated that she was the daughter of King Erik Eriksson.
[1] The Danish genealogist Sixten Otto Brenner made the same claim independently in 1961.
Brenner noted that Ingeborg's seal featured three leopards, the symbol of the Danish royal family, which Erik had inherited from his mother.
He further supported his claim by citing the papal dispensations required for Ingeborg's daughters, Helena and Elisabeth, to marry Count Günther IX of Schwarzburg-Blankenburg and Duke Valdemar of Schleswig, despite their fourth degree of affinity with their husbands.
[2] He also noted that Birger's other daughter Rikissa is referred to as filia regis Suecie in Chronica principum Saxonie, and the same papal dispensations would have been required for Ingeborg's daughters as for Erik's.