It's "does she have a car?" --
The verb "does" here is the main verb, so it's what's getting conjugated according to the subject "she" -- that's why we say "does" instead of "do" -- "she does," not "she do." The other verb then just stays in its infinitive form completely irrespective of the subject, since the main verb has already accommodated the subject. The infinitive form is "have" ("to have," not "to has").
Do I have a car?
Do you have a car?
Does he/she/it have a car?
Do we have a car?
Do you (plural) have a car?
Do they have a car?
Ashley Newman-Owens
GMAT Instructor
Veritas Prep
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