I would guess that she got in the middle of two dominant male dogs that never should have been anywhere near one another in the first place. These aren’t the kind of dogs that just anyone can control let alone a pack of them.
That was my thought when I read "she was also babysitting a Presa for a friend." I wouldn't be surprised if the strange Presa got into it with one or more of her dogs, and she tried to break it up, with tragic results.