The Air, with caveats
As a gift, you may be the only one looking at the options in advancebut it would be a good idea, in person.
The MacBook Air is more than powerful enough, and as distinctly the lightest the best choice for someone who will be frequently traveling with it. Also stylish. BUT, if a higher resolution than the MacBook Pro, its screen is otherwise subpar.
Compare these side by side and you should quickly notice the difference. The retina is definitely the best; and as not much heavier than the Air, a good portable option as well (if more expensive, and some Version A teething issues, or also the issue of Haswell on the horizon). But between just the MacBook Pro and Air, the former superior in its screen. Also, for that matter, more power for the money, as well as ports. But distinctly heavier.
The Air still has an okay screen, just not in comparison to the others. Your wife may not particularly notice or care. Should she, then plan on using your 14 day window to swap to something else.
A further kicker in this is the promised advent of Haswell likely in Q3 2013. It should make a decided difference in such as the 13" rMBP. But the Air should benefit as well, and may see other notable revisions with this coming change. All of which would suggest waiting for it. Since you cannot exactly, perhaps consider a refurbished Air for nowand the promise of a shining new one when out.
It could be worth the wait. And in the interim she'll have a chance to fall in love or not with the Air.