It's hard for me to tell that something is there. But I'm also one that doesn't really believe in ghosts either. I've experienced odd things, but I usually don't put much into it. I have no doubt though that you're mother is seeing something and believes in what she is seeing. Is it possible that the energy that she is feeding into these occurances/appearances is making them stronger to her? I'm not suggesting she's losing it, but do you think it may be kind of like that 'feeding the beast' theory? And if she's afraid of talking to whatever she believes is in her house, have you tried for her, if for no other reason than to just ease her mind? Or do you think that perhaps she is the most sensitive to it? This is very curious.