If you want particulary destructive say "No its fine I couldn't even say anything since you were doing all the talking".

Honestly though you're only engaging with her from time to time and at family get togethers, no need to like her just try to be amicable. You could just ignore it but also let your husband know your concerns, if she needs something limit her dependence on your husband for all these tasks and sometimes just be unavailable.

As the skipper says: http://25.media.tumblr.com/tumblr_lozvhoXbXh1qffj5lo1_r1_500.gif

Beyond that you could practice your witty remarks and comebacks and could engage in a passive aggressive war of words everytime till she cuts stops doing this. But honestly is it worth the effort you have to put in? Some people just have that kind of disposition and aren't self aware. Even you try this method it might not change much.