It is difficult to know what her diagnosis may be but bipolar disorder or schizophrenia are realistic possibilities. Your fiancé’s mother does not seem well. She seems as though she is actively symptomatic. She seems paranoid and possibly is experiencing delusions or hallucinations. She may have those symptoms because she is not taking her medication.
Research has shown that approximately 50 percent of individuals with bipolar disorder or schizophrenia do not believe they have an illness and subsequently refuse treatment. If someone does not believe that they are ill, then refusing treatment seems logical to them. The problem is that they are clearly ill even if they aren’t aware. Unfortunately, individuals who are symptomatic suffer tremendously and so do their families who struggle with how to deal with a loved one who is clearly sick. It is a very difficult situation.
If someone isn’t taking their medication, then their family and friends should encourage them to do so. It can also be helpful to become actively involved in a loved one’s treatment, if possible. For instance, a close member of the family could offer to attend a doctor’s appointment with your fiancé’s mother, if she is agreeable.
You asked whether or not it is safe for her to fly alone. If she is actively symptomatic, then it would not be advisable. She might be okay but maybe not. I would not recommend it.
With regard to bipolar disorder and schizophrenia, scientists believe there is a genetic component. Scientists believe that there is a strong environmental component as well. Science has not determined the definitive causes of these mental illnesses.
Research shows that individuals who have relatives with schizophrenia or bipolar disorder are at a slight increased risk for developing one of these disorders. Having a relative with the disease in no way guarantees that other family members will develop it. Again, the risk is slight and its development depends on many factors.
Don’t hesitate to write again if you have additional questions. Please take care.