Perhaps she's not only blind but hard of hearing as well? So when she "sees" shadows coming through the door or coming towards her, she just doesn't know who it is because she can't really make out that person's face or hear that person's voice.

Please beg your Mom to take her to the vets. Perhaps you can show her all the posts people made here on PT. Maybe that will convince her.

Good luck & keep us posted on her condition.