I don’t think it has to be one or the other, he can hammer on this now and then concentrate on her lies later....
She is BOTH mentally deficient AND thoroughly dishonest.
No, not really. You stick with the truth (that she lies) because you don’t want to compromise your own narrative.
If you make the charge that she’s crazy, all she has to do is to not appear crazy. Then it looks like both sides lie, so six one way, half a dozen the other.