how involved are her parents in making sure she's educated on the care of these animals and actually doing what's needed?
I don't know that she's a sociopath, but she's certainly lacking in spontaneous empathy. sometimes folk are just seriously undereducated about what to do.
I had animals growing up, and no parental supervision. I happen to be a rabid self-educator, but most folks aren't. we lost animals from improper care when I was a kid, out of my lack of experience. if I hadn't been teaching myself we'd have lost a lot more.
if she's unsupervised on the animal care, and her parents aren't knowledgeable or interested in becoming so, and she's not a self-learner, any animal she takes in is at real risk.
on the goat subject, it's not rare for male goats to get urinary stones. it is aggravated by diet (too much alfalfa for instance) but it can sometimes happen in ideal circumstances, and it may or may not be treatable, depending on the situation. it can kill them. so what she said from the vet sounds approximately correct. and she did take the animal to the vet, which lots of inexperienced and uncaring folks won't do.
maybe what she needs is someone to teach her.
so it looks to me like you've got three choices.
- a polite "no" to selling her animals, or an excuse like "I don't have any to sell right now".
- a polite "no" and a reason why (she doesn't educate herself enough before she gets an animal, and that's not fair to the animal), along with some suggestions as to how to be better prepared and educated before she gets the next animal.
- a little investment of your time in helping her learn what works and how to better educate herself. introduce her to forums like this or BackYardHerds. find out about local 4H programs and encourage her to join. invite her over and show her how you care for your birds and talk to her about what matters, how to get help, how to consider what the animal feels and needs, how you go about educating yourself.
the first will save your animals from harm.
the second and third may save many other animals from harm as well.
if she really had an emotional attachment to the goat she lost, you've got a window of time where you may be able to get her to pay attention and do things differently. it may not work, but maybe its worth a try. I realize you're not close friends, but maybe for the sake of the animals, it's worth a little of your time. and if she's not interested in learning, you'll have your answer about the cause of all the animal deaths.