They're designed for dogs who by the nature of the sport pull and lunge and are more substantial than a normal harness. You should also be able to find one that's padded. Try looking at www.fordogtrainers.co.uk who sell harnesses for boxers as well as other breeds of dogs.

I would also suggest an additional fence or gate or something to make absolutely sure she can't get near anyone. Where we live if a dog attacks in public the owner can be arrested and the dog destroyed depending on the situation. I have one pup who's dog aggressive and one pup who's people aggressive, so I say err on the side of caution.

I'd look into getting some real sheepskin covers made for the harness to cover the areas that rub. The problem you may have is time between events for the rubs to heal? There are a number of things you can get for that and if you have to use it whilst the area is still sore and before the sheepskin is ready, maybe talk to your vet about a suitable cream that will allow the harness to slide instead of rub? You could also find a good saddler that will make you a made to measure harness (with enough adjustment for changes in weight and muscle tone) made from a soft leather. then you just need to treat it to keep it soft and subtle. Maybe helpful, I am trying to think outside the box!

I can't help but think you need to slow things down for her; I hear what you're saying in that you can't get out of these commitments, and she can't be left on her own, but she has been through so much in her life recently, it sounds like these events is just one thing too much for her to cope with.

Could you look into putting her into boarding kennels, or with a home-boarder, for the times you're at the events?

I'm very lucky to have a wonderful boarding kennels run by an ex RSPCA inspector that I use; the staff there really understand dog problems and work WITH owners, continuing with any work you're currently trying to do with the dog. But you may find that a dog-boarder is a better bet, if you don't want to put her back into a kennels situation. Many dog-walkers also home-board, and often they have knowledge of dog-behaviour training techniques, too. You'd need to do your homework and make sure your dog was in safe hands - it will take a bit of time to find the right dog-sitter.

It's something to consider anyway - a bit of breathing space might be good for her AND for you!