
She sounds hugely stressed (as do the others a bit, with the incessant barking). The first thing you need to do is to stop shouting at her - all that is doing is adding to her stress and upset (as she is showing by running to her bed and being quiet). She's already on edge all the time by the sound of it - shouting will make that worse and could escalate the small things you are seeing now to full fights very quickly because her stress levels will simply go too high for her to cope. She is trying to communicate - listen to her, don't gag her.
Next, can your dogs see this GSD? If so then I would suggest blocking the view to reduce the stimulation of it pacing up and down.
I would then suggest doing some counterconditioning - make the presence of the GSD a predictor of fun things or tasty things, if your dogs are foody (and I would do it with all the dogs, as she may well be picking up on stress from them too, making her own even worse).
On walks - again, stop telling her off, you will only add to her stress and make it more likely that she'll do it again/more. Try distracting her, then rewarding her when she's doing it right - lots of fuss and praise/food/play/whatever works for her.
I have direct experience of the difference that telling off vs. rewarding can do a similar situation and with immediate effect either way - River gets quite stressy when the other dogs play, and she will badger them, barge them and have a go to stop them. If I tell her off, she'll do it more, because her stress levels are increased by me and it comes out in this behaviour. If all I do is fuss her and play with her when she comes away from them, she does it a LOT less because she is happier and can therefore learn and make better decisions.
Re. the food - put her out of the room while you're preparing. She is clearly struggling to cope with the excitement of it with the stress this GSD is causing too, so don't leave her in a situation she can't cope with.
I would speak to the GSD's owners too - but not as a confrontation. It may be that their dog is as worried about yours as yours are about it, and they may want to find a solution as well.