A good idea to have your wife go out on her own/with instructor and get some sailing time in!
Fear, oh yes, knowing what is frightening and dealing with it--both important factors. Getting to the bottom of what is causing fear and unease with sailing is very important. Finding ways to get a partner to deal with whatever the fear is all about --without giving up sailing! is important, too. Of course, some folks just don't want to be out there sailing. In that case, the person may use a natural fear as an excuse since then they don't have to admit that they're just really not interested in a sailing life. Conversely, some people say they just don't want the sailing lifestyle when really it is raw fear that is keeping them ashore.
While I can't imagine just not being interested, I certainly believe that we all have our preferences for lifestyle and if your wife doesn't want a sailing lifestyle for the next decade or two, having the conversation openly without laying a guilt trip on her would be pretty important. The reality is that many people will only engage in sailing for a short (a few years) portion of their life and if a partner is presented with the idea that "we're going sailing for 2 years and then we'll evaluate" the partner is much more likely to be into the idea of the sailing (for 2 years) rather than making excuses not to go in the first place because they're afraid they'll be "stuck" with only a sailing lifestyle forevermore.
Well, that's just my opinion.
On a related note--while my husband and I work together and play together well, there are many issues with sailing where I am more cautious than he is. He's an adrenalin junkie whereas I can get my thrills "on the cheap" so to speak. Given our disparate tolerance for scary things, we communicate alot and deal with things as they come up. If life isn't naturally thrilling enough, he starts doing risky things; if life is getting too thrilling, I start getting whiny and/or demanding. If he has to excessively curtail the thrills to meet my demands, he starts getting snippy. Realizing our tendencies, we can joke about it. When I suggest to him that maybe he needs to go hang upside down off the bowsprit in the bow wave (while sailing un-reefed in 38 knot winds), he gets my point quickly and is willing to take a reef.