Per Bobson-Well, let's look at it logically. There are three possibilities, and a smattering of other, very unlikely possibilities (or if you prefer, two likely possibilities, and just move #3 down to the very unlikely list). You know your wife better than any of us.
1) She's just being generous, recognizing that you want the rifle.
2) She wants something in return; a material item, perhaps? (minivan, house add-on, etc)
3) It's a guilt-gift; she did something wrong (or plans to) and wants to buy you the rifle to help make things right, whether you find out what she did or not.
Unfortunately in my case it ended up being No. 3. Should have went for the Browning Citori instead of the Ruger Red Label, in retrospect.