Thanks Lewjam for bringing this post to my notice. I think though that the the other posters have probably covered the likely options reasonably well. However I would say that if this bird is otherwise Ok and you like her it's a pity to give her away without trying to break this behaviour. Most behavioural problems have a husbandry cause, boredom, too close confinement poor feeding, nutrition or some such so let's start by ensuring these issues are in order.
You say when you put their food bowls in the run, so straight away I'm wondering is this the problem. Chx are browser feeders and so you should be feeding them ad libitum which means they should have food available ALL the time hung up in gravity feeders not ration fed in bowls. So get 2 2.5 kg gravity feeds like this.
http://www.chicken-house.co.uk/acatalog/3kg_Orange_and_White_plastic_Chick_Feeder.html#a1517and two similar style drinkers.
Three bantams should eat no more than 200grams of feed a day tops so put around 1Kg of layers pellets in each and hang them at back height under cover protected from rain well separated so the agressive bully can't defend both at the same time. Do the same with the drinkers but stood on the ground.
Cut out treat feeds in the afternoon and stop meal worms for the time being, just give one handful of corn each scattered about so one can't guard all in the EVENING only.
If these measures don't work fit the bully with a beak bumper bit so she can't feather peck and it will slow her eating down too. Lock her in the house while the other eat if necessary and she'l soon improve. Chx eat only enough for their needs so they shouldn't over eat.
I think what you are doing is encouraging their natural survival behaviour which any animal in a flock or herd situation will develop which is that if food is rationed they will attempt to monopolise it. Our pigs do this too and if we treat feed the hens the dominant ones will attempt to drive the other away so they get all the goodies. Stop ration feeding and stop treat feading for the time being and it'll sort itself out I'm confident. I doubt it's because one bird is so stand offish that it won't mix.
I've actually had someone bring me a hen to look after over a holiday like this which was very aggressive to other birds and refused to eat anything but grapes and treat feeds and poultry mash. Two weeks later when she returned it was socialising normally and eating layers pellets like the rest. The owner had developed these problems by allowing the bird to dictate to her. If you understand their natural behaviour you can learn to get it to work in your favour instead of reinforcing their bad habits.
Best wishes
HF