sounds like you're doing great.
to me, ducks are easier to tell boys from girls. the only way i can tell mine apart is the boy is bigger. but then i've never picked either of them up and hung them upside down for a good inspection. lol
did you run errands in the car she sits by or a different one? i think she takes the car to be like a tree or bush, protection. it provides a shadow and she could run underneath it if necessary.
if you are into it, i would feed her. she might take a shelter you built, or she might not.
i...