Me again. :-)
I'm not stalking you, really.
If you want to talk to Dr. Lupo, you need to ask your question here;
Your step-father is the fly in the ointment. You could have a county nurse, or home healthcare worker, or public health come in and evaluate her, but not if he won't let them in the house.
Somehow you need to get her to the doctor with you in the exam room.
The bottom line is, if he is more competant than she is, he needs to assume the responsibility of making sure she takes her meds. It sounds like he doesn't care if she takes them or not.
Maybe you can sit him down and tell him in a loving way that if your mother dies because of his neglect, he will be in some scuzzy nursing home within a week.
Maybe he is past scaring, and is not competant enough to care for her.
A very difficult situation.
You know my experience with my Mother and my MIL. Caring for elderly parents without stepping on their toes is very difficult. I hope some of the other members here have helpful suggestions. You are not the only one dealing with this problem.
Best of luck to you.