I used to BE that annoying friend to one of my friends once, but I never knew untill way after I realized he was making up excuses not to do stuff with me, and just plainly began disliking me without my knowledge. Unfortunately it all ended bitterly, we never spoke again after I tried to start a fight with him after I learned he was talking behind my back.
I say just plainly gather yourself and your wife and tell her the truth, tell her that she needs to moderate things and that she's just too close for comfort, and give her time to get over it.
The only problem is if she's psycho, maybe she'll kill you because she'll force herself to think you're preventing her from being better friends with your wife
, in that case you might need to put yourself out of the picture.