One downside of using co-wife is that if you forget the hyphen the eye can see it as cow-wife, which of course is not flattering at all.
Seriously though, Ginny brings out a great point about a woman's need to be honored as "wife." That's one of the hardest parts of current marriage laws (especially in areas which have "proports to be" married statutes) -- that you can't legally use the term wife in reference to any subsequent woman without divorce entering into the picture. Otherwise it would be easy to co-opt terms such as "life partner" and the like - which mean essentially the same thing - but subtly demean subsequent wives.
Seriously though, Ginny brings out a great point about a woman's need to be honored as "wife." That's one of the hardest parts of current marriage laws (especially in areas which have "proports to be" married statutes) -- that you can't legally use the term wife in reference to any subsequent woman without divorce entering into the picture. Otherwise it would be easy to co-opt terms such as "life partner" and the like - which mean essentially the same thing - but subtly demean subsequent wives.