Have you checked both driver and passenger side lower control arms? both of mine were worn down after 230k miles and i would get wheel shudder every time I came to a stop and again when I let off the brake pedal. You can see the wheel shimmy if you are viewing it from outside. I replaced both LCA's and that solved my problem. I also got the dreaded knocking noise whenever going over any bumps or uneven surfaces on my right side.
What year and mileage is your wife's Tribeca?