I'm with Dana and Grav.
It sucks when kids give their crappy-other-parent a pass, but it helps to remember that when you add up all the years, they have had to put up with more of her crap than you have, and they will have to continue dealing with her crap even after this particular tempest. They may know all too well that making a big deal about this will only make their lives harder in the long run.
If this is the kind of person she is, then she would not feel bad even if confronted anyway. She would either double down and accuse you of lying, or find a way to make up a better lie next time so she will be believed. Better to treat her like the child she is. A smirk is always more powerful than a yell. Oh, and make sure you dance very happily with your beautiful wife all night long.
