Anti]would definitely recommend 9mm if you're wife's gonna use it.
9mm and .40S&W is mostly supersonic(unless buying weaker subsonic rounds), while .45 is subsonic unless you load up some crazy +p rounds. So .45 is not quite as loud. That is something else to consider. The .45 is about 850-900 fps(most rounds). It moves slow like firing some lug nuts at someone. It really comes down to personal preference.
Take her to the range and give her a full size 1911. I am confident she would like the .45. I haven't met a woman who hasn't.
