AIBU to ask a friend’s guest not to join private breakfast?

From your description I presume she thought you were early too and came over to join you.
Turning her away ,even if you did it politely which seems to be doubt , was pretty rude and hurtful. You need to have your private conversations somewhere you will not be interrupted. The fact that you dislike her is actually irrelevant to the incident ,although it probably had an effect on your behaviour. Would you have sent another friend you liked away ?

Your choice to have a private breakfast at the location of the group breakfast is bonkers. She, reasonably, came to join you and you were unkind. Okay you don’t like her but you made her feel bad because you’d got a plan that she wasn’t aware of and unknowingly interrupted. Then you didn’t go and see the group despite saying you would.

the only reply can be “I’m so sorry there was a miscommunication yesterday and I confused things by meeting ‘Jane’ first for a private catch up before the group breakfast. It was a bit of a sensitive conversation but I didn’t mean to cause upset or for anyone to feel bullied. I was juggling meet ups and it didn’t quite work out. I won’t do that again.”

She wasn't though. The group were meeting there. The OP was part of that group.

I’m confused. The friend you met for breakfast, are they part of the group? If so, surely it would be weird any other group member arriving sat elsewhere?

She was invited though. She just arrived a bit early and assumed it was the group meet up.

I think your attitude was a bit harsh frankly and bordering on rude especially if you were all meeting at the same place.

If others have an issue with this woman then you should agree to tell the intro friend that she was in the wrong for bringing her into the group. If you're the only one with the problem though, you're going to have to deal with it.

How do the other people in the group feel about her?

It’s infuriating and upsetting, but you may need to leave the group if it’s just you who doesn’t like her.

I get that it's annoying when a boorish person joins an established group and tends to dominate the conversations.

But I think what you said, unless it was with a polite apologetic tone was quite rude and nasty. I've been in the position of being the person who went to greet people I knew and been quite bluntly "sent away". It's mortifying. If your conversation is that private, you should be having it in a private place.

If you’re going to a venue to meet someone there and they are already there, it would be pretty bloody odd of you to sit somewhere else!

Yes - this is what I don't understand.

Are their two uninvited guests/"friends" or just one?

If there are two, which is which?

And why arrange to meet a friend for breakfast at the meeting venue, and then tell her she has to leave!?!?!?

Why should op make her self have to change venues to avoid the Boor deciding she wants to force herself on people?

If my reading is correct and you met breakfast friend in the same venue as the coffee meet, then you're being a bit precious. Why not meet somewhere else? No wonder other woman was confused. You sound rather black and white in your thinking.

I think when someone uses the word plonk, it means they hate them.

@Ano1n Set up a new group!

Well surely it’s a social norm to not plonk yourself down at someone else’s breakfast uninvited

Actually I don't think it was unreasonable, depending on how it was said. If you said, in a nice voice, something along the lines of 'actually Sandra and I are just having a quick catch up before we meet with everyone else as we have something to discuss privately' then I think that's perfectly reasonable.

if you said, in a cross voice, 'do you mind - this is a private conversation' then you were definitely being unreasonable.

Was the person you met for breakfast part of the group? Because if that's the case, the new woman probably came to join you as she just thought it was the group meeting. She didn't do anything wrong and probably felt embarrassed and hurt when you told her to go and sit elsewhere!

Is there only one cafe where you live? Go someone else.

I think if she came into the place you always meet and you were there already she’s not unreasonable to approach and attempt to join you. You were very mean if you said anything like you reported here. You should have very gently said something like “hi lovely to see you can you grab the usual for the group, x and I are just having a quick 1to1 chat about something and will join you all at the usual time.”
but frankly it’s weird to have a private conversation in the same place you know 5-10 people you know are going to be dribbling in looking for the group.

Gatecrashing someone's breakfast should be a crime. I'd also be fuming op.
Maybe add in the group that you are enforcing your own boundaries and that also should be encouraged..

I read this as you were having breakfast with a friend who wasn’t part of the coffee group so boor didn’t know them? If so, it would then depend how you said it whether you were rude or not (and I suspect your face or tone gave away your dislike!). If you said, oh I’m sorry Boor, we’re just finishing off our breakfast and have some personal things to discuss would you mind if I join you for coffee with the others in a bit and give us some privacy now? Then def not bullying but still awkward. Social norms are that you accept boor in and give up on what you were discussing, sorry. Or you could have moved yourselves out…

I can understand the frustration if you don’t like her and were genuinely trying to have a private conversation but I imagine it came across as exceptionally rude and akin to school yard “you can’t sit with us” exclusion.

IMO the appropriate thing to do would be to continue the private conversation later.

"Sorry for hurting your feelings Jane, but I was having a sensitive and private conversation with someone else at the time when you wanted to join us and I tried to be as polite as possible to protect everyone's feelings in the moment.

Next time, I'll meet her elsewhere rather than give the impression we were there for the main meet up two hours early, ".

Cant believe you choose the same time and place for your private meeting no wonder she thought she could join you