My Grandma thought that people thought she was the president (or at least high up in government) and were mad at her for building the wall.

I'm sorry. It is likely she is suffering from dementia. It is a brain disease that can begin in old age. Alzheimer's is almost identical to dementia. Basically what happens is that brain cells are systematically destroyed by a certain kind o protein in the brain.

My own mother died of dementia. Eventually the brain becomes like swiss cheese, and the sufferer does not have enough left for the organs to function.

Delusions or wild stories are a symptom of the disease. For example, my father was deceased, but my mother would tell me that he had come alive again, and that he had gone on a plane and the plane crashed because he had used a cheap airline, and now he was dead again. The next day she would tell me she had called him. The day after that she would tell me that she was on a train, and the train was moving all the time.

If your grandmother is not receiving medical treatment, it might be a good idea to suggest to your mother or father to help her get the treatment she needs. There are new drugs now that might help or delay the progress.