I've just discovered Aldonza is my direct ancestor, so I've been tracing her family on Wikipedia and other sources. There seems to have long been confusion about her parentage but the most recent documentation seems to be:
"In a document of 1182 recording a donation to San Prudencio de Monte Laturce that survives only in a Spanish translation by Gaspar Coronel, Aldonza calls herself a first cousin (consobrina) of Rodrigo Álvarez, son of Álvaro Rodríguez and Sancha Fernández de Traba.[15] It is most likely, then, that she was a daughter of Sancha's brother, Gonzalo Fernández de Traba. She is known to have had close relations with Gonzalo's other children, Gómez and Urraca. She was a daughter of Gonzalo by his first wife, Elvira, a daughter of Rodrigo Vélaz."
Which, as you can read, would make her a niece of the couple attached to her as her parents,
