Do you have friends that ride that can talk to her about riding? Are you prepared to 'armor up' every time you ride (and I mean every time)? Have you taken the MSF basic rider course?
I am lucky in that my wife understands why I ride and has since started riding. Most people get their impressions about motorcycles from people that have no clue about riding and therefore harbor preconceived notions. You have to convince your wife that you will be a smart, safe, capable rider. And then you just have to wear her down with incessant whining!!
"Never underestimate the power of human stupidity" - Robert Heinlein