Oh dear, your sister should NOT be owning a pet now or maybe even for a few years. Right now, she is financially challenged and it sounds like she doesn't realize the responsibility that comes with pet(DOG) ownership. I know she is your sister and you love her dearly. Perhaps you can type up a letter that addresses these few issues:

1) That she is currently in a financial ditch and perhaps cannot keep up with the expenses of a dog.

2) Is the dog fixed and up to shots? If not, then I would advise her to either do it now or seriously consider relinquishing her pup.

3) Laughing at an animal's misery is not something appropriate of a dog or ANY pet owner. Does she want this dog or not? To me, it sounds like she's a "keep-it-till-it-loses-its-cuteness" type, A.K.A. one who should not be owning an animal.

4) If she wants to keep Jade and truly does love her, then she has to commit herself. This involves paying and attending obedience classes with a passion. This also involves regularly visiting the vet, regularly taking Jade for walks and runs (that's an easy one), actively incorporating Jade into the family and house, and finally, realizing Jade is a living, breathing creature that needs love, compassion, and a responsible owner.

And finally add that you are her sister and you love her. If your sister decides to keep Jade, you will help with her problems and always be there for support. I'm terribly sorry that your sister has decided to go this route, but I wish you the best of luck in correcting your sister's ways. Good Luck!!!!
Edit: I just saw Cyber-sibes post and I have to wonder, is your sister the type to get offended if you point out her problems with Jade? Or is she the type that doesn't quite care so much about the dog? If she is the former, then you should take a more comfortable/casual line of attack like a visit to her house and non-chalantly mentioning Jade's problems.