Whatever you do keep the first flight short, local (so you don't get lost) and steady: best in calm weather obviously or early morning/evening.
Safety brief essential but don't make it too scary, make sure she's had a pee before you take off and the minute she says she's had enough, go home.
Mrs Cusco went up with me in Warrior piloted by everso slightly cocky 17 yr old son of Cusco, a month after his PPL, a few years ago.
A bit hazy and a few steep turns later Mrs Cusco had had the cr*p scared out of her so much that when I got my PPL a few years later she steadfastly refused to fly in a SEL again.
A moments lack of consideration and Cusco now spends many a weekend flying sans Mrs Cusco when it could have been different.....
Treat your pax with care and consideration at all times.