Ah, xort beat me to it. I second his comments.
Use the charter as the bait, if she bites, set the hook and get into separate lessons when you're sure she's engaged and shows an interest in the "doing" part rather than just the "going" part. Depending on your cap'n, you or both of you will be given ample opportunity to participate and learn, (provided its not just a quick sunset trip around the harbor), or be allowed to just sit back, sip your painkiller and just go along for the ride. I for one love it when my guests offer to participate, and the ones who do, and show interest, get invited back.
Signature picture courtesy of Cal20 Class Assn.