"VAERS is not reliable for determining causality, since it's a passive reporting system. That means anyone can report. Even people who might have only read about it on the Internet. It also very clearly states that its data does not imply causality. Just because X is followed by Y does not mean X caused Y. To assume so is a logical fallacy (post hoc fallacy)."
Because I know that arguing with her about her beliefs is like talking to a wall. She isn't going to hear me. She's cherry-picking the data she looks at and ignoring the data she doesn't like, and then trying to make people feel bad by comparing those who "don't believe in medical choice" to Hitler, Mussolini, and Kim Jong-Un. My hope is that by sticking to facts (nothing I said was actually wrong or could be twisted to prove either side) she will at least start considering the interpretation of her data.
Those hopes are low, though. Most anti-vaxxers rely on the post hoc fallacy to justify their beliefs. I can only scream, "Correlation is not the same as causation!" so many times before my frustration wins out.