I feel like I've failed dd and have broken one of the most important 'rules' in my head that she shouldn't touch a drop of alcohol.
I understand, OP, I really do. My dad has severe OCD and I’ve definitely inherited some of those tendencies too. I frequently set ‘rules’ for myself and then beat myself up mercilessly when I don’t stick to them. The thing I have to remember, though, is that those rules are only important in my head and they don’t actually affect anyone else in any way.
You’ve already said that you aren’t worried about your daughter actually being physically harmed by the alcohol. So now you just need to keep reminding yourself that this ‘rule’ you’ve broken is yours, and yours alone. It is of no ‘real’ consequence and means nothing to anyone else, including your daughter.
Imagine someone was raising their child vegan and then they accidentally gave them something with a trace of milk power in it. They might be annoyed with themselves, of course, but then they’d just make a note not to buy that product again. It would be totally pointless to get themselves worked up about it.
I know it’s so, so hard but please try to take a step back and a deep breath, and get some perspective on this. You haven’t fucked up, except by the very high standards that you, and you alone, have imposed on yourself. Try to forgive yourself and focus on more important things, like the love and care you show your daughter every day.