Is she just doing it to please you? If so she is not going to
change her mind about comics no matter what.
If not since you know your wife likes and dislikes you are the best judge
to select what ever she might enjoy, what I would do is pretty much what you suggested
a self contained story with out too many reference to continuity, art is also very important
you need some thing she might understand and appreciate at first glance and again
only you know what see might like.
Good Luck.