Sounds like a control issue to me. You can always find something "wrong" if you want to, "jerking [her] head" sounds suspicious. If you're driving like an eedeeit all the time I could understand this, but being respectful of your passenger and still have a jerking head problem seems a little exaggerated. "Stiff ride" sounds like a problem for a geriatric with hemmoroids or arthritis; more suspect control issues if you ask me.

By way of comparision, my current wife (who's not a thrill junkie, nor a control freak, BTW) was in the passenger seat when I reported the first-time 135mph velocity on the highway when the car was new said without looking up from her magazine!, " That's nice dear."