CantThinkofFunnyName - oh dear, sorry you are suffering the wrath of the egotistical PTA mums!
Sounds to me you did nothing whatsoever wrong and even if you did which happens when you first get into things this woman could have acted more adult about it and explained how "she" likes it done.
My friend who got involved with her PTA for the first time last year had an awful experience with this nasty mum who was so controlling and intimidating.
It was a shame because my friend decided to no longer be involved in the PTA after that. It seemed all the other mums were scared of this woman and were happy to go along with her way.
My PTA luckily are nice people and I was just thinking how the would react to this and I actually remember when I was involved two years ago (been too busy since) that we all had each others emails and would circulate ideas, like adding to a list. They were not kept as TOP SECRET! So this woman at your school just sounds really controlling to me.
I would not play her game and argue your case back as that shows to her there is a case to be made with this. I would just tell her to chill out and its no big deal the ideas were revealed as "our ideas!"... Just say that you didnt realise something so small would bother her so much and if she prefers you could resend it out as "HER NAMEs IDEAS"
Dont allow her to intimidate you.
Its not worth getting your lovely belly all tight and you upset. Few deep breaths and tell yourself, "It does not matter".
Hold your head high in the playgroud, you didnt commit a crime