I'm sorry to hear about your father.
If the will was not witnessed and was not completely in his handwriting, then it is not a valid will. When there is no valid will, the estate passes "intestate," which means there are statutes that explain what happens.
Intestate statutes do not give anything to someone who is not a family member, Moreover, if the title of the car is in your father's name, and this person is not on the title, she has no claim to it.
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