Does insulting one's sister and speaking of her misbehavior towards her mother, in her absence and with the mother sharing in the complaint, constitute backbiting that necessitates sin?

Disobeying one's parents is one of the gravest sins, and Allah and His Messenger (peace be upon him) have forbidden it, threatening the disobedient with exclusion from Paradise. The right of the mother is emphasized in righteousness and obedience. Therefore, the sister should remind herself of the severity of disobedience, and the questioner should supplicate for her and offer advice through beneficial books and audio recordings. The questioner should also ask her mother to supplicate for her sister, as the supplication of a parent for their child is answered. As for what occurs in one's mind, such as curses without utterance, there is no accountability for it. The questioner's conversation with her mother about her sister, for the purpose of seeking advice, is not considered forbidden backbiting.