Is listening to a friend talk about her mother's actions, which the friend describes as harming her or hindering her affairs, considered backbiting, even if the listener tries to make her think well of her mother? And what should be done in this situation?

The Prophet, peace and blessings be upon him, defined backbiting as: "Your mention of your brother with that which he dislikes." So, if your friend mentions someone with that which they dislike, it is backbiting, and it is obligatory for you to forbid her from it.