I believe is dementia with jealous delusions. My mother accuses my father of having affairs. He is 83, she is 81. None of her accusations are true, but she believes the created scenarios in her mind. How do I get help for her when she refuses to get help and believes if my father will get rid of his "girlfriends" all will be well. How can he get help when he is constantly bullied?
You can't "make" Mom see her doctor, but maybe you can trick her into it.
Meanwhile, give her doctor a written list of your concerns. The infidelity delusion is primary, of course, but are there other behaviors of concern? Is her memory failing? Does she have other obsessions? Any changes to her depth perception? Her sense of smell? Is she repeating herself a lot? Unless she has given permission her doctor will not be able to talk to you about her case, but that doesn't mean he or she can't listen to your concerns.
I am generally in favor of going with the flow for dementia delusions and hallucinations. When my husband saw bats in our bedroom I didn't argue with him. But when he accused me of stealing his money I did not "admit" it. I was really afraid of breaking our trust bond. I honestly don't know how I would have handled the fairly common infidelity delusion. Probably along the lines of "I'm so sorry I've done anything to give you the impression I've been unfaithful. I didn't mean to hurt you. I'll try to be more careful so I don't give false impressions. You are my soul mate and my one true love. I would never have an affair!" But mostly I would bring it up with his doctor.
Your mom refuses to go to the Dr. You can't force her to go. You know your dad isn't having affairs but you said your mom just wants him to admit it and get rid of these imaginary girlfriends so they can move on. Do you think your mom will really let it go if your dad admits to this? If so, have him admit to it. But you're taking a huge gamble as your mom may start to obsess about something else that is equally unpleasant.
It's a crazy solution but with dementia we have to think outside the box and get creative sometimes.
He will most likely refer her to a neurologist to determine if it's dementia..