Your much better off to skip the Kel Tec and stick with a conventional pump or semi auto shot gun.
Nothing wrong with it per se, but you and your wife are just getting into guns, the KT seems to even give professionals problems, I would not want to learn on it. Secondly is the price issue, you can get a Maverick Arms (Mossberg made in Mexico ) for about a third the cost of the KT. Third issue is after market modifications, there aren't any for the KT.
As to the Knoxx recoil absorbing stocks, it recoils "funny" with the whole gun sliding to the rear instead of pushing you.
If recoil is that much of an issue go with a semi auto since cycling the action soaks up a bit of the kick. I would definitely get an "M-4" style telescoping stock, even if your wife never shoots it, it allows you to compensate for things like heavier winter clothing.