What is the difference between does have and has? For example, compare she does have a car and she has a car.
Based on my understanding as a native speaker (London, England), normally you would say "she has a car."
However, if you want to emphasize that it's not true to say the she does not have a car, then you would say that she does have a car.
In general, the difference between has and does have is simply that including the modal auxiliary verb do adds emphasis (which can also be achieved by intonation alone, but let that pass for now).
Thus, "She does have a car" might validly be used in various contexts. For example
British speakers often use get as the auxiliary verb - "She has got a car" - again, adding emphasis.