I'm not quite sure what you are asking. Is this how WHAT starts? Dementia? You said she's experiencing dementia, so I would say that it has already started. I will tell you that everyone's experience is unique. Have you asked her why she is nervous? What does she tell you? I think that if the day comes when I begin experiencing severe memory loss, I will also cry.
Have you taken her to the doctor about this? What does the doctor say? Has she had any memory testing? She might do better with an anti-anxiety medicine. It might calm her down some. I think I would start there. Best wishes...
Another thought: This kind of behavior could also be associated with depression, with or without dementia. Another reason to see a doctor. Depression is treatable.
Have you taken her to the doctor about this? What does the doctor say? Has she had any memory testing? She might do better with an anti-anxiety medicine. It might calm her down some. I think I would start there. Best wishes...
If it is a medical diagnosis I suggest talking to the doctor who made the diagnosis and asking about possible treatment for her crying and nerves.
If it has not been medically confirmed, then I think the starting point is to see her doctor and have a complete evaluation done.
Either way, this is a behavior to discuss with medical professionals who understand and have treated dementia.