OP, I can only offer this simple bit of advice: you need to move on. You can send your cousin the link to the terrible stocking choice she currently possesses but after that just let her deal with it. You've done a great job in offering her sound advice and it's admirable you show a great deal of compassion toward her fish but there reaches a point when further intervention is not worth it particularly if it is putting a strain on your relationship with her or your personal life. There are millions of fish that live terrible lives in extremely poor living conditions. There are also millions of cats, dogs, cows, chickens, humans and countless other organisms that suffer the same fate. We can do our best to help one another and help our fellow animal friends but
we cannot force someone do the same. You can educate them, offer advice, and lead by example but ultimately it is up to them. Many people unfortunately are just not very bright and need to learn the hard way (sadly at the expense of others). On the bright side there is at least hope that your cousin will learn from this experience. Perhaps she will do more research into things and realize what she needs to do to make things right, or perhaps she will realize that this hobby simply isn't for her. People everyday come to that same conclusion when they buy cute puppies and kittens but then realize they're not cut out to take care of them. Sadly this happens quite often with human babies, too, but I digress. In the end just don't let this particular event ruin your week. Quit dwelling on the drama and instead be upwardly mobile about things. Launch yourself forward past these sort of things by doubling your efforts to educate newbies on the forums, spending extra time maintaining your own tanks, increasing your knowledge of this wonderful hobby... and call it a day.
