Nothing, because if the village contains only 100 married couples then the adulterous husbands don't have a greeeeat deal of choice who they cheat with.
As a result, any woman who condemns the unfaithful husband would be the person he'd cheated WITH and would likely be ostracized by the community (regardless of the fact they are likely all guilty of the same scenario). This would also explain why, if every other woman knows a husband is cheating, they don't tell the poor woman. This is also assuming from the wording that the law the women would never break is the 'killing your husband' one.
Equally, if the men are all cheating with each other then it raises a secondary problem of proving it as it would require finding the two women who didn't know there was some extra-marital snuggling going on.
Alternatively, they kill all the husbands as they're all cheaters.
I'm leaning towards the first option, they have to be cheating with someone and unless all 100 are closeted, there are some pretty important questions about the wife's fidelity which also need answering.