Honestly, I'm not sure. I don't think it was good for her to eat it and she'll probably get sick later as well. I remember when my first dog dog ate a pigeon that she'd caught because it was injured (I came home and found feathers all over my yard and put two and two together), she threw up later that day and refused to eat or drink. I was going to take her to vet the next day, but then she started to eat and drink like normal and she got better all on her own without vet assistance. So, if your friend's dog gets sick, then don't panic right away. She probably just needs to get the fish out of her system, like humans do when they eat something bad, too, but if she doesn't get better like mine did the next day, then take her to the vet, esp. if she gets worse.