Sorry op, I hadn't read your updates earlier!
The assistant head is behaving disgracefully!!! Unfortunately I have been on the receiving end of this tactic and it is not pleasant! I advise that any future communication is in writing (preferably in email) this will hopefully stop this head from behaving so manipulatively!
I have been accused of 'demonizing the school through its figurehead', just for pointing out previous agreed actions that had not come to completion! I didn't bother replying, I went straight to the Head's boss, as in Scotland that was the Quality Improvement Officer at our local education department. I wrote out a timeline of what had been going on, as well as attaching several emails where Head had been rude and unprofessional. I included the fact that as a professional myself (primary teacher before health declined), I was disgusted at her attitude of superiority towards myself and my husband.
Thankfully the QIO was horrified and the HT was forced to apologise to me in writing and in person. It might have been forced but it allowed me to get my point across!
In your situation, I suggest that you write a timeline of events. Gather copies of the school newsletters demanding money. Write an account of what happened with your friend, both on her visit to the office, then when you accompanied her. Then write an account of your meeting with HT (including the intimidating environment, intimidating voice, the constant 'I feel attacked' when you were being calm and reasonable and her refusal to listen to what you were saying) Explain that you felt incredibly intimidated to the point you ended up in tears and apologising, when you had nothing to apologise for!!!
Mention their text which is far too little too late! Make sure to list policy/ law that you know is being disregarded here Ask also why the school are not utilising the pupil premium which is available for each child who qualifies for free school meals! As a school with half of the pupils entitled to free school meals and therefore the pp, it seems ridiculous that poorer families are being pressurised for money!!! The pupil premium is there to fund this sort of eventuality!!!
Then contact the board of governors / education department (depending on your location) and ask who you need to speak to in order to make a complaint about the intimidating behaviour of the assistant head and the fraudulent and disgraceful pressure being placed upon financially vulnerable families!
You need to complain, the assistant head is a bully and is sitting smugly, thinking she has intimidated you into silence! When you get a reply, its likely that the assistant head will be copied in on the email! Don't worry, they won't want to lash out in front of their boss!