If I was you I would complain to:
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Send them a copy of the letter.
Question why a charity is using funds to sue people.
Question why a charity is making the lady suffer and upset her.
I would contact all the media I could, not just in the USA but UK, Germany and so on.
I would write to all your politicians, send them the letter and ask why a charity is allowed to act like this.
If this was the UK, and a charity did this, it would be front page of the Daily Mail, and the next day they would probably end up shutting down.