how should i respond to this

there's a woman who lives near me, a young woman, and every time i pass her in the street or pass by her house and she's on the doorstep, and she sees me, she coughs loudly and exagerratedly...and it really bothers me as i don't know her? and i think- is she being too familiar with me? when i don't know her?

otherwise, why cough out loud every time she sees me? how should i respond to this?