Is an aunt's complaint to her sister about her husband's injustice considered backbiting (gheebah)? And what is the ruling on a mother or aunt assisting in communication in this situation, such as providing a mobile phone, its charger, or a phone number?

Backbiting is forbidden but may be permissible for an overriding benefit. The default is to interpret the mother’s request in good faith and with a positive assumption, and to grant her what she asks for as an act of piety towards her, in accordance with His, the Almighty’s, saying: "And your Lord has decreed that you shall not worship except Him, and to parents, good treatment." You should not refuse her unless you are certain that she is seeking your help in something forbidden, for it is not permissible to assist in it, in accordance with His, the Almighty’s, saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression."