The overriding principle with TERFs is that they hate men with every fiber of their being. Seriously, that's the gist of it. They see trans women as men who are trying to invade women's spaces for nefarious purposes, and they see trans men as poor brainwashed women that internalized so much misogyny that they deluded themselves into believing they aren't actually women. Nonbinary people just get lumped into whatever box corresponds to their gender assigned at birth.
The irony is that all this trans hate always inevitably blows back on cis women. Cis women like my wife who I cannot tell you how many times she's been harassed in the restroom because she's got broad shoulders, an undercut, and a very Butch Lesbian aesthetic. Or my daughter who when she was around 2 a lady tried to steal a baby doll that we were going to buy her while loudly proclaiming that she should be the one to buy it because her daughter (emphasis hers) really wanted a baby doll and there were none left. This lady straight up thought we had twin boys but we just let one of them wear a dress because my daughter wanted her hair cut like her Mommy and had a really short undercut.
Livestreaming the encounter could also potentially work. But yeah, ideally you probably want as many different camera angles and recordings as you can.