I'd tend to think that Thelesie is a variant of Talésie.
I've first come across Talésie as an old Québécois name and managed to trace it back to the Kingdom of Aragon and the Crown of Aragon (Talésie de Montaner, born 1080, for example, was the granddaughter of
Odon de Montaner).
It is noteworthy that both today's Basque country as well as the region of modern-day Provence belonged to the Crown of Aragon.
Now, the name Talésie seems to be extinct in
France, but lives on in the Basque region in the form of Talesia.
Both Talesia and Talésie are forms of
Adelaide.
Formerly
Capucine