Bookshelf Speakers For 350 Or Less?? new & used

The Mission 731 you mentioned is a sweet little speaker and would probably fit her needs perfectly, I think there are some used ones listed on a-gon.

Are you wanting to spend the 350, thats something you have to addrss. There is a pair of B&W 302 right here on the site,posted yesterday, for 135 + ship, thats a very good deal. I have a pair of Conrad Johnsons SL21's of JBL L20t's for 175 that I think is a good value(duh) The Missions 731's or the NHT's are great as well. These are all available under 200 in my book. I honestly don't think you need to be DIYing it for someone not familiar with audio, females tend to be a little pickier than guys. And the Spica's, which are great, aren't what I call real rugged and don't move or ship well, as the voice coil's are at a very tight tolerance.
350, if you spend it all, takes you to another realm, in my opinion. The small Maggies like the SMG's are available for that used, another great value. There is also a pair of Proac Super Tablettes and a pair of Rauna Tyre on this site available for 350, both incredible loudspeakers.
You could buy a few of the above and some decent stands and cable(all used) and still get out for under 350. I guess it is harder than it sounds like.

I own Paradigm Titans. Used them in office system with NAD reciever, for the money can't be beat. About $225 brand new for the pair.

You might find a pair of Vandersteen 1B's for that price. They are excellent, but perhaps too large to strictly be considered "bookshelf."

Certainly the sound of the 1B is excellent, as are many of the above suggestions.

I would look for (used) Triangle Titus xs or Dynaudio 40. Or get her to pony up a little more cash for pretty little Silverline SR 12s. She might develope an affection for one of these nice sounding AND attractive speakers, sparking a new love affair with all things audio.