Hi, I'd like to help you with your question.
There is no physical condition that would cause a person to emotionally deny events that occur or twist them around in any fashion. Although memory loss during the later years is common, it can only be related to conditions of the brain including Alzheimer's and dementia, as well as other specific brain disorders. These disorders can cause a person to become combative and argumentative as well as uncooperative and unable to see reason. The person can also confuse the facts of the situation, but usually it is not with intent, but rather genuine confusion.
If your mother has twisted facts around and been combative all her life, then a physical condition is unlikely to be the cause. What you are describing sounds more like a personality disorder. A person who doesn't deal well with facts and twists things around to tell a more appealing story where they appear to be cooperative and good usually has a personality disorder. These disorders can occur when the person, during their formative years, did not have their needs met by their caregivers. So in order to cope, they developed dysfunctional ways to deal with their environment. While these ways may have worked when they lived in the situation, they no longer work when the child becomes an adult. But since the adaptive behavior is all they know, the person doesn't change it. Their behavior becomes a problem to those around them.
Your mother can change how she reacts, but she needs to see that there is something wrong with how she is acting. Right now, all she sees is that she can create problems then come out looking like she did nothing wrong. It is frustrating to those around her and makes it difficult to communicate and interact with her.
In order to cope with your mother, you may need to change how you approach her. If she is uncooperative with you, find others she may be less inclined to act out with. For example, if she respects her doctor, ask him/her to help you explain the situation to your mother. Then she may cooperate knowing that her doctor will be checking up on her. You can also minimize your reaction to her behavior. People with personality disorders get most of their energy from others' reactions to their behavior. If you see her becoming upset, leave. Then try again later. If she keeps getting upset, keep leaving. She will eventually see that she is not getting to you and calm down.
Family therapy can help if you feel that everyone is being affected by your mother's behavior. Having support and learning ways to cope with her can go a long way to helping you feel better.
I hope this has helped you,