I tend to agree with jaye on this, the hawk is just doing what it needs to to eat and survive and there isn't a whole lot you can do to stop that. I have a chicken hawk hanging around at times and he also picks off small birds, and as heartbreaking as it is to see, I think it also wises up the other birds to predators so they don't fall victim. Predators are important for teaching birds to be more cautious (a good thing), and I can't blame the hawk for doing this, although I would prefer if he targetted some of the mice and rats in the area instead, but he is an awesome creature up close, quite menacing looking but just as the doves have a right to feed and exist, so do the hawks imo. we get squeamish about animals killing other animals but this is just part of life out there in the wild. he's a meat eater and other birds are a big part of his diet and as bad as I feel for the birds who get taken, I try to accept this as part of the natural cycle of things and I try not to put one species above another in that regard. perhaps you could tell the woman that this is just part of the natural scheme of things and that other birds will become more aware of the danger (I suspect this is why my hawk comes and goes, the birds wise up and it gets harder to catch them, and then months later he comes back again).
ps. I do know the feeling of wondering if he was going to decimate the small bird species in my garden, but it's never happened, I suspect he grabs the ones which aren't paying attention when he strikes (he hides in the garden and quickly flies up from behind to grab them when they are perched somewhere, he's quite clever in how he does that so they don't see him coming) but this is how nature works, the strong and the fit survive, while the weak get taken out. It sounds a bit cold and heartless, but nature has a plan in everything it does, and it's far better for the strong and clever to survive for the species.