Liv knows all too well about infidelity, so this case should be easy. First the rumors aren't true according to Robbie, who said via Twitter: "There's absolutely no truth to the ridiculous rumour in Star mag." So there's a plus there. Then there's evidence that the couple is in pure bliss with their photos in Las Vegas.
Liv would suggest Jada and Margot have a girls night on the town to further validate that there's nothing going on. It would make an incredbily huge statement if we saw Jada with the woman alleged to be with her husband.