When asked about being possessed by a ghost or haunted, what is the victim's state? I suspect that my mother is entangled in something and talks to herself about invisible things every day.

Take your mother to the temple. There are "immortals" in the temple. Please invite Guanyin Bodhisattva at home. Your mother may be weak and encounter something unclean. When your mother wakes up, ask her what she has caught. When your mother was ill, she knocked on the bed with a broom and cursed the possessed ghost. This is a folk way to exorcise evil spirits. Let your mother sleep in the bed and put on red clothes. Your mother should also wear red clothes.