It definitely takes two hands to floss, but that leaves her elbows free for steering.
Case closed.
I steer with my knees when I’m driving and flossing.
My favorite driving and doing other things while driving story was when I saw a guy in LA on the Santa Monica shaving and driving. Not with an electric razor, but with a face full of foam shaving cream and a little yellow Bic razor.
I almost drove off the freeway laughing.