Her hagiography, written by Serbian Archbishop Danilo II (1324–1337), states only that she "was of a French family" (Serbian: бысть оть племене фpoужьскaаго), while in hagiography of her husband, King Stefan Uroš I, the same statement was repeated, but it was also added that she was "from the imperial family".

[3] By the beginning of the 20th century, several genealogical theories on her origin were proposed, based mainly on examination of historical data related to Helena's sister, or half-sister Maria and her family.

[6] That theory was based on free interpretation of some sources from the 1280s and 1290s, showing that Angevine kings of Naples referred to Queen Helen of Serbia as dear cousin.

soror), or at least a half-sister of Queen Helen of Serbia, thus focusing their efforts on discovering key details on Maria's ancestry.

[8][9] Key napolitan document that points to the sisterhood between Maria and Helen was issued in the summer of 1280, by king Charles I of Sicily, who allowed lady Maria to travel from Apulia to Serbia, to visit her sister, the queen of Serbia (Latin: Quia nobilis mulier domina Maria de Chaurs cum filio suo et familia eiusdem domine intendit transfretare ad presens ad partes Servie visura dominam reginam Servie sororem suam).

In later documents, issued in 1281, Maria was mentioned by king Charles as his cousin (Latin: nobilis mulier Maria domina Chau consanguinea nostra carissima), and widow of Anselm of Cayeux, who was son or grandson of the elder Anselm de Cayeux (Latin: nobilem mulierem Mariam relictam quondam nobilis viri Anselmi de Chau).

[13][14] Several scholars have accepted McDaniel's conclusion that Maria of Cayeux and Helen of Serbia were sisters, or at least half sisters, thus also accepting his approach to complicated questions on Queen Helen's ancestry, and by proxy to other genealogical questions, related to their ancestors and cousins from various families (Angelos, Courtenay, Cayeux).

She proved to be a successful administrator, governing regions with mixed Serbian Orthodox and Roman Catholic population.