ime there's pretty much nowhere to go with these people. I've convinced some waverers that it's dodgy on the basis of the links with BNP and other far right groups, and by showing the evidence from trials of people getting convicted for not paying council tax, but try making an argument with FOTLers about how it doesn't even matter if they are right, the courts/police/prisons have the legal monopoly on violence and if they want to nick you, they will, regardless of whether you call yourself BIGTOM or tom of the family big.
Also went through the magna carta nonsense with one of them, and asked him why, if they were right, had they not got their 15 nobles to challenge the king's rule? He said they had 15 nobles, I asked when they were going to challenge the King and he didn't know. Wouldn't give up the idea that the Magna Carta still gives this right though, and still insisted it was relevant anyway in today's parliamentary age.
Leave it imo. Don't bother. Let her get taken to court and found guilty.