I have a friend who owns a Cherokee ... for the longest time his wife would not fly with him. Then, she'd only do it on VFR days in smooth air. Then, she'd go IFR with him. But recently, she's refusing altogether. When they travel, he flies the airplane, she takes the airlines, and they meet at the other end.
As to your situation ... ask her why she hasn't flown with you ... if she's afraid, find out why. Maybe a good intro would be for her to backseat an instructional flight with you ... so that there would be two qualified pilots up front, might put her at ease. Talk to her, try to work it out ... if you can, great, if not, well there are always some people who just don't want to fly in small aircraft. My mom was that way for a long time. Then, I showed up to pick her up from an overseas flight in the Duchess, and she had no choice but to ride along. Since then, she's decided that she prefers flying with me to riding the airlines.
Good luck ...
FL270