I think the point you raised was very valid and had I been in the group going, I would have wanted to know too...but if you have apologised for being honest about the venue, because she is a good friend and you could be direct, thats also OK, but you didn't go direct, you made an open comment on the group chat and she will have felt criticised and undermined . Also from the sounds of it you started off with "I'm not going" which would have instead of "I'd love to come but can we change the venue". You should have told her privately about the rating and allowed her to announce the issue.
Presumably she will now be inundated with lots of the invitees asking what is happening so she won't be a happy bunny.
So from her stand point, you have apologised for stating you are not going as its 1 star but she probably needs to hear that (from your own explanation given here), you didn't deliver it well and that with the benefit of hindsight, you should have messaged her privately to alert her to the problem?
And give her a few days to calm down and rethink the situation. And if she doesn't come back to you, she is being petty!
Just out of interest have any other persons that have contacted you to say thanks, have they said if the venue has been changed?
As I said before, your rationale was great, it was the delivery that was poor (from your own admission) and it seems you have apologised for being honest when its the way you said you weren't coming publicly, that would have been the embarrassing part for her. do you see what I am saying - you went in a bit heavy.