I have to say, we have no idea what the comment was that was upsetting.
It could have been transphobic.
It could have been saying that you can't change sex etc etc and this be deemed as transphobic.
We don't know really.
As sad as it sounds, there's two elements to this - a very distressed mother who would easily be upset and 'transphobia' effectively being a term that has such a broad span depending on whether you are an activist with a low threshold as to the definition or if you take the term on a much more restricted and dry legal definition.
So I'm not going to read any more into it than that - I certainly don't think that MN is the worst place on the internet. I do think she could have read any number of appalling comments on FB on accounts from Warrington.
She was upset and distressed. Thats understandable. Social media can be horrible for ANY public issue involving awful events. Those were the comments she saw.
I think targetting MN over and above anywhere on the basis of this isn't helpful and doesn't actually prove anything as much as some would like.