To not invite sister to social gathering

Can she go to your work Christmas lunch too?

Its a Christmas meal, time of goodwill and all that and she is your sister...Unbelievable.

Be big hearted, let her join in

Stick to the group members only.
Your mother was rude and presumptuous to do that.

I’d say to your sister that your mum was mistaken and that the meal is just for practicing members of the hobby group to ensure it’s fair to all. However, there is still time to join the hobby group over the next couple of weeks, and that you’d love her to give it a try,

What on earth is this 'can't possibly tell you' hobby?
I am trying to imagine a 'lifestyle' hobby that would immediately identify the person doing it - and that you would want to talk about for a whole meal?
I belong to a yoga group (which I suppose is a 'lifestyle' ) and we have regular meals out. Not only do we allow other people to come (daughters etc.) but we certainly don't talk about it all night.

I think it sounds like a MLM scam 🤣

I have follow up questions for you @NoSourDough - has your sister actually expressed an interest in attending this meal to meet with these other group members or is this your mother trying to act in the best interest of her daughter here and by doing this she has actually made it more difficult for the other daughter?
Has your mother a history of doing things like this?

Using this as the basis for the social event, can other group members invite their relations and relatives to the event if they aren't part of the group themselves?

If the answer to that is no, then you're well within your rights @NoSourDough to talk with your mother, tell her she overstepped as far as the social event is concerned and that unfortunately, until your sister actually participates in the group, she can't attend the social events with the group.

Tell your sister too that you can't extend an invite to her because that would set a precedent for others to have an open invitation and this is an event for the group only but she is still more than welcome to join the group itself and she will automatically get an invite that way.

i don’t see the problem tbh. I mean, it’s like saying the others would be pissed off if she came along to one of the regular sessions as a newbie. Instead, she’s coming along to the social. Just say she’ll be joining in the new year and you’re introducing her now.

I hope the hobby/lifestyle group is something spectacular, like being a witch.

You’re not on your own because I’d also think it wasn’t on. Open to anyone or open to members only.

The solution is she comes to at least one group session before the Xmas party

I agree with you OP.

but firstly - does your sister even want to come? Personally I’d feel more anxious about a social event with lots of strangers than I would about going to a regular hobby evening with my mum and sister where everyone is doing the hobby!

secondly, I’d talk to your sister - it sounds as if you get on - and kindly explain what you’ve said here and suggest that if she does want to come to the social she comes to a meeting or two of the hobby in the run up to it so she will know some faces at the meal.

I think you’re being mean. You’ve said your sister has no friends and lacks confidence. This might give her the push to join the group once she gets to meet everyone. Unless they are really snooty and un accepting.

I'm in a similar group. We had a couple of people ask if they could come to a meal we were having (it was mentioned in our local magazine). We were unsure but said yes. As it turned out, they got to know the other members in a relaxed environment and they now all come regularly and a couple more people they know now come too.

It's been really good for us as a group, and had we said no to the original request they may never have joined.

I'm in the don't invite her camp. Just let her know she's welcome to join the group and then attend the event as a member.

Or get your sister to rejoin before the dinner!

Thats a great idea. Have a dedicated bring a potential new member gathering

Your mum has placed you in a tricky post as you are group leader and the rules will have been bent for your family member, which is not fair and might piss a few people off who might also have liked to invite a plus one. And will equally piss off those who see the dinner as members only. There’ll be a bunch in between who don’t care either way.

in your shoes I’d cancel your sisters place for the Christmas meal, but arrange an informal social event in the new year at which plus ones/ prospective new members would be welcome.

everyone would be happy to have one extra there that's not attended before due to low confidence

How do you know ‘everyone’ would be happy? You don’t!!

Last thing OP needs is a group of people annoyed that the sister was invited outside of the group and they weren’t given the same option. They may well have family/friends who wouldn’t otherwise get a Christmas meal out.

Then suggest she comes to a meeting before the meal?

Your sister is struggling to make friends. You've invited her to the group and she hasn't felt able to make it. If she can attend the meal she might then feel able to come to the other meetings. If you're worried about being unfair to other members then let them bring a friend who might be interested in joining.

Have a chat to your sister and explain that this Xmas dinner is for group members only. If she wants to come to the dinner, she needs to become a regular member of the group first.