Fear of doors?

Question
My family rescued a 4 to 5 year old West Highland Ranch terrier named Bella. Bella seems to have assimilated to the family pretty well and pays attention to everyone except my older sister, Maggie. Maggie has Cerebral Palsy, can't talk and is in a wheelchair. Bella acts as if she doesn't exist, she doesn't even follow us into her room on the main floor when we're all in it. I sometimes call her in there but she doesn't seem to stay in there very long. We did have our 15 year old Tibetian Terrier die a month ago and she was often in Maggie's room and even slept beside or on the guest bed with my mom. We had our carpets cleaned a week before our old dog died, but perhaps it still smells like her? But that doesn't explain why Bella ignores my sister in other rooms. Is there a way I can get Bella to care about all the members of the family?

Answer
Bella may not have been socialized to anyone with a disability when she was a puppy, so avoids this "novel" situation for her own protection.  One way to make her more comfortable around your sister is to feed Bella some tasty treats any time she is in your sister's room with her.  If your sister can manage to toss treats onto the floor for the dog, all the better, but it will still help if you do it.  What you are trying to do is create for Bella a positive association with being in your sister's presence.