AIBU for making DD12 give up her treat for eating more than her share of a takeaway?

I think this is on you and your DH OP. You know your elder DD is a big eater (or 'greedy' in your words), and that she has often tried to take more than her fair share when sharing food. You should have paused the movie for a few moments and supervised the sharing out of the food. No good trusting a child with no self restraint to moderate.

With my DSDs, we always asked one child to split the shared treat into two (or serve the other), and then the other would choose which one they wanted. Both very competitive and on the spectrum, this was my DH's fantastic idea to stop arguments! That way no one could grab more than the other.

The punishment isn't for eating 28 edamame, it's for taking something belonging to her sister, and depriving her sister of something she was looking forward to. It's for showing a lack of consideration to her sister.

No, but hopefully you'd be punishing for leaving her sister in tears with only 2, while she ate 28 of them when she was told to share?

Out of interest @SongsOfSongs what consequence are you getting for effectively giving your DD11’s side to her sister?

You said you already knew that DD12 has problems around food and self-control and she has a history of eating more than her fair share. You asked DD12, the one with food issues, to split the meal and when she said no she would be reasonable you said okay because it would take less time (I.e. you took the easy option rather than the option you knew was the right one based on history).

Lo and behold, history repeats itself, DD12 eats almost everything and DD11 loses out. You knew this was likely to happen because it’s happened before and that’s exactly why you make them split the food.

I think this one is on you, OP, for lazy parenting, not protecting DD11 and setting DD12 up to fail.

Is she over weight too.

When you knew she was a suckker for gluttony why ask her to share a side out? Take the control away from her.

And yes make her buy her sister something with her own money. Frankly I'd stop the extra £1 until she can control her eating.

More than likely mindless eating as she has food issues. Not that OP cares, OP set her up to fail, bring her to a therapist, don’t scold her.
I really feel for this child.

The OP has already said it was edamame pods.

I wouldn’t be punishing for eating 28 Edamame.

I think I would've perhaps bought the sister a treat with the older child's pound the very next day, rather than waiting until Wednesday, and rather than expecting the older girl to buy her sister a treat (if she has problems with self control, there's a good chance the treat won't make it home to her sister). But in principle, I don't see anything wrong with the punishment.

I think it's ridiculous what people are saying about it being wrong to punish a child over food. You're not punishing her for being hungry, you're punishing her for being selfish and taking something that belonged to someone else, and depriving her sister of something nice. If she was still hungry after eating her share of the takeaway and side, she could've had an apple, a yoghurt, a bowl of cereal or a slice of toast. You're allowed to be hungry and you're allowed to eat until you're not hungry anymore. But you're not allowed to take someone else's treat when you've already had yours. I can't believe some people are arguing with that.

This is a lesson though, that you must always split things up for them from now on, and that's OK. Even now, I always divide sharers onto separate plates for me and my husband, because he's a slower eater than me and very much a gentleman, which just means I'd end up scoffing 3 quarters of it if we didn't each have our own plate.

Oh it's that old old saying again - you know what a mother's place is ...
IN THE WRONG!

These are teenagers, not toddlers. Learning to share sensibly is a life skill that they need to develop.

I'd worry about ED to be honest. Being this greedy to the point that she didn't consider her sister's needs is worrying. I feel your "consequence" is strange, just reinforcing that food is a reward/punishment and getting her sister to have both her snack (I presume) and her sister's doesn't address the greed issue at all. An honest conversation about food is what she needs.

Yes, greed is greed and just because people hate the word, it doesn't mean she wasn't greedy and didn't deliberately take almost all of it, leaving her sister with almost none.

Not only is it greedy but it's selfish too.

Of course the OP shouldn't call the child greedy to her face, as dealing instead with her behaviour is a better way forward.

But denying this was greedy and selfish behaviour isn't going to help anyone.

From now on, one gets to split the dish and the other gets to choose which portion they want.
It always helps the split be equal.

Bear in mind they do grow a crazy amount at that age - kid sized to adult sized often happens at 12-13 so I guess that does take an awful lot of extra calories.

But as someone with a problematic relationship with food ie not eating enough for years, developing a phobia of eating in front of people at 11, then over eating much of my adult life, it's easy to pin the word greedy on a child.

I was chatting to friends, one of who's daughter has issues with food, another friend said her daughter who's older recently told her that the school has an issue with girls being nasty to others simply for eating and that the daughter used to hide to eat her lunch!!!

Agree. What did you order? Without knowing exactly its hard to say OP. Yabu order more food next time.

Your DD was 'born ravenous'?

And you are still surprised 12 years later that she has a bigger appetite?
If it really is huge, then have you ever asked for medical advice - thyroid, diabetes etc been checked.
Is she overwieght?
Otherwise, just accept that some people eat more than others.

What is your relationship with food OP?

But she was greedy though. She didn't accidentally take one or two pieces more than her fair share, she ate 28 out of a 30 piece side knowing she should share it with her sister.