The symptoms of MS depend on the patient. Some of the symptoms can manifest this way.
Without looking at her MRI and knowing her history I wouldn't be able to say whether it was directly directly caused by sclerosis in a behaviour centre, as an indirect consequence caused by sclerosis, because she is annoyed with life, etc.
Ok I'll edit this as you are getting some really stupid advice in this thread.
You have to think what the mechanism of MS is. Area of the neural network eg spine + brain are systematically attacked at varying intervals causing damage and potential malfunction in that area. There is no real pattern to how it changes people because it really depends on which area is attacked. Eg attack on the optic nerves - sight depletion (this is common but actually indicative of lesser severity), attacking say C5 spine then you may get tingling at the finger tips and shooting sensations down the limbs whenever the neck is moved. So it really depends on where this woman has had the damage does it not? She may for all you know have had her behaviour centres attacked therefore changing her behaviour etc. I am sure you get the picture.
What you need to forget is muppets who say they know people with MS and they don't do this. Great for those people who will have a different pattern because they have been attacked in different areas. Those people may not have to have lived with the life this woman has.
That is not to excuse the behaviour - just give it a frame of reference.
I would say in my experience (which is considerable in this field) that people with MS have in the main significant problems that would manifest as frustrations, mental health issues, anger, factors associated with fatigue in the later stages. However, I have not really met people who I would consider to be complete and utter ***** unless they actively undergoing a "relapse" in which case their behaviour may well be out of their control.