So, to show someone is lying, you need to show that the person knows it's untrue and is claiming it to be true.
If she's giving an opinion, as you say, then she, by definition, is not lying.
In any case, WillRockwell is making the definitive statement that her statements are lies, so if that's true, he should be able to point out exactly how.
Otherwise, he's just making a completely unsubstantiated claim. (WillRockwell? Imagine that.)