what can I do, if my mother has been diagnosed with dimentia? One doctor said she can' t be left alone, can't drive, or work.

You might consider attending an Alzheimer's supprot group before starting down the path of a guardianshp. If that does not give you sonme ideas, you need to file for a guardianship in the county where your mother resides.  It will be a very painful event for you, your siblings and yoru mother; but if your mother will not cooerate with you regarding her care and well-being, you have no choice but filing for guardianship.