Most likely redirected aggression.
This is what happens when dogs are scared or super frustrated, highly aroused (in the 'wound up ready to go' sense not sexually... usually) and are restrained in some way, in this case on leads.
With nowhere to go and tension rising, they will lash out at whatever/whoever is nearest and that will be each other and likely the handler.
For this reason too, a dog in a fight may well bite their owner when the owner shoves a hand in to separate, they don't realise what they're doing and just bite whatever is there.
So several big dogs and little dogs, yapping and barking and pulling and one snaps at the other and someone snaps at her and she falls down, its very very easy to see how they just get stuck into whatever they can reach and the more she becomes a dead weight on the end of that lead, up to a point the more they will bite.
Another really dangerous factor is that when a dog is in a fight and has hold of another dog or person, they may not let go - to let go in this situation is to allow their opponent to get a better grip on them, get another grip, so they don't let go.
This is not a breed specific thing this is an individual specific thing, any of the dogs could have done this and if they got her in the neck in the wrong place, she could have bled out fast. Even a Dachshund, if its grabbed and won't let go you'd need both hands and to be standing up to get them off. She was down on the floor under multiple fighting/grabbing/holding dogs.
If you did overpower a smaller dog biting down and not letting go, then the outcome is huge amounts of tearing trauma to whatever they had hold of, so even if you have the strength to rip off a smaller dog - the damage they'd do could be fatal.
Humans are fragile things, the jugular vein is superficial and unprotected, unless a dog has no teeth at all, any dog could pierce that with ease.
I think theres been a significant lack of respect and understanding for what dogs can do, what dogs will do, how dogs behave, and it's been going on for some time. It'd be easy to lay blame at the feet of the 'furbaby' types but honestly, the 'I've got black cargo pants, military boots and a Cane Corso with the ears sliced off it' type 'dogs a dog, my dogs a weapon' types are too - because they believe somehow their dogs know right from wrong and know a good guy from a bad guy... and that their dog won't turn on them. And they use the type of training more likely to cause aggression and serious errors on the dogs part.
It's people we need to educate, and control. Then the dog issue will resolve.
But its much easier to ban breeds, which as I said earlier, has been proven not to work but is what the well meaning but ignorant public cry out for.