Woman on holiday? AIBU?

What a shame it took a child to try to make poor Sarah feel better. Take a leaf out of his book.

Because she said her daughter was fat like an elephant.

The 6 y old just repeated and here OP had her chance to protect Sarah and tell her 6 year old "Remember we don't comment on other people's bodies, it's very rude."

And none of you said anything, either to support Sarah or to tell your dd she was being unkind.

So Sarah probably thinks all the adults agree with her mother.

and

Your dd thinks it’s ok to call people names and laugh at mean jokes because no adult has told her not to,

Great parenting, shame you have started a thread criticising someone else’s parenting!

Sarah's mum compared Sarah to an elephant. That can lead to eating disorders.

OP, the big question remains: why on earth did you not correct your daughter?

Op started a thread about it! No one is covered in glory here apart from the son who tried to be kind. But let's not blame a little girl for continuing a toxic conversation that an adult started.

Can anyone explain to me why Sarah’s mom is horrible? 🤔
Maybe I fail to understand it as English is not my first language.

As I read this story, nobody was nasty here. The 6 year-old was just being a typical 6 year-old, they usually point out the obvious without filter. If anyone, I would pull her mum (OP) up on it, as she failed to explain to her on the spot that it’s rude to call someone fat when they can hear you.

Sounds like you were also trying to ‘please’ the adult by not calling out your DD awful behaviour.

Well, I don’t believe it. There’s no sympathy for poor Sarah in your posts.

Exactly.

And what has a 9yo having breast issue got to do with anything?

It sounds like OP agrees with the fat shaming.

So basically three other adults chose not to challenge the mother or defend the child in the moment and instead left her feeling withdrawn and upset.

The mother is indeed toxic as you describe. The rest of you need to take a good hard look at yourselves as well. It wouldn't need to be aggressive, a simple 'Gosh that's harsh, did you really mean to say that out loud?" Would have changed the tone and shown your daughter that it's not okay.

You need your daughter to stop calling people fat.

As a teacher the mantra 'we don't comment on something people can't change in 30 seconds' (i.e 'You have fluff in your hair' or 'your cardigan is on inside out' is okay. 'You're fat' or 'you have a big nose' is not)
It's been quite effective.

I don't think your 6 year old did anything wrong. She's 6 and if she hears an adult saying something 'naughty' she will think she has permission to repeat it.

And as much as we all say we will call people out, sometimes when it's something really shocking, it can take a while for your brain to catch up and think of an appropriate way to do this, particularly if there is a third party involved and you don't want to embarrass them further (eg if you'd said something and the mother took it as an invitation to get into a debate about whether the girl is actually fat or not, that would have been mortifying for the poor girl). Ideally you could have said something like 'well I think she looks lovely and she is a nice kind girl and that's more important than looks' type thing...but again if say the mother had just snorted, it's not going to help.

The mum is clearly an awful awful person. I'm not sure I'd avoid her fully though for the sake of the girl who needs some kindness

Well, it sounded very much like you were more put out that your son was putting 'the blame' on his sister as against the mother. When most decent people would have been horrified immediately at what was said, corrected the daughter etc.

And you seem pretty blase about her behaviour at dinner, and obviously previous occasions when he has been rude to your son.

Why didn’t you correct your child when they laughed?

Why didn’t you say that was mean and we don’t say mean things?

You’re not upset about what Sarah heard at all, you’re just upset about your own dc. That’s disgusting.

what further context though? It had already all been said?

This is vile all around. That poor 9 year old. A 9yr old girl may be beginning puberty at that age and weight gain and development may come ahead of a growth spurt and periods in the next year.

I'm afraid you sound somewhat judgemental of the child's weight too as you dont appear to have challenged the mothers comments in the moment or explained to your daughter her comment was unkind. Interesting that only your son appears to have tried to console the poor girl and its not his job to recognise the mothers part in this. If you were the only other adult present that's on you.

That poor little girl. And shame on you for not correcting your daughter. That was a teaching moment about kindness if ever there was one.

I don't really understand what your 9 year old's comment adds to your question?
Why do you think that's relevant?

It comes across as though you're blaming him for not blaming the mum?

If your AIBU is "to now have realised that Sarah’s mum is a rancid toxic bitch?" then DS's bit is neither here nor there (other than demonstrating he seems to have more emotional sensitivity and kindness than anyone else at the table, including all the adults).

When were on a trip to another town yesterday the other mum got tipsy and said at lunch - all 7 of us were on the same table - and the mum pointed to an elephant in a book my daughter was reading and said “Sarah’s as fat as that”. -

My daughter giggled and repeated it and I could see Sarah’s face and she was very upset

At which point you should have said that's not very nice, made your dd apologise to Sarah and made your excuses to leave then have nothing more to do with that vile woman. How sweet that your ds tried (the only one out of all of you) to make Sarah feel better when she was visibly upset by her mothers cruel words.