Considering that AuRel told such words after watching Wistala, and considering that he spoke of a "Mother", it's highly probable that Ayangthe was indeed AuRel's sister when he was still an hatchling (thus making her a Skotl).
Nothing is known of her fate, during the AuRel's life in Lavadome and after his departure.
AuRel's words Edit
“Ayangthe, I’ve hurt myself on the slate pile. Jumped too far down. Is Mother asmelled?”