Everyone, ACoA or not, does something embarrassing at some point. My guess is that your friend didn't even notice.
Have you found your center again?
The likelihood is that if you found your center and are able to be with your friend, she won't remember unless you remind her. People have short attention spans - especially when they are concerned for their own well-being.
If you have found your center again, I'd bet that you could go over, be with your friend, never bring the issue up, and she wouldn't remember. ACoA's are great at remembering everything they ever did wrong. Healthy people? They don't remember those things as strongly.
If you truly want to move past this, the best thing you can do is process what you think got triggered, deal with it internally, forgive yourself for being human and slipping up, and be with your friend again. She likely hasn't thought twice about it, while you've been unable to forget it.
That's been my experience at least. Let is slide, the Universe doesn't keep a tally sheet on how many times you've goofed up and it's not going to go on your permanent record. Accept that you slipped, forgive yourself, move on.
Your friend will appreciate your support far more than she probably wants or needs an apology or explanation.
If you can't get past the trigger, then it's time for some outside intervention (therapy/AlAnon/whatever works for you).
(I know this sounds blunt, it's not intended as a chastisement, but as a "here's what works for me" Take what you want, leave the rest)