Petfinder.com is a good one, full of dogs (and other pets) that need homes through rescues
many of the online puppy sites, create badly bred, sick puppies to sell :/ not a good place to find a dog for your sister. Pet stores are just as bad. I was in her shoes when I was younger, my parents got me a dog from a petstore, died 4 weeks later after paying thousands to try to save him
If your dead set on a young puppy, and dont want to try a shelter or rescue, try looking for a GOOD breeder one that does health testing, loves her dogs, doesn't have THAT many puppies, etc..
Ill see if I can dig up a good breeder for u, I dont know much about jack russells, but someone more knowledgable here is bound to help you out with that
the dog world i very different from the horse world.
YOu are much more likly to find a sick and poorly bred dog threw online purchase than you are a horse. because dogs are easier to breed and there are less laws about keeping them.
First off you should be looking at what you want in a dog.
all dog breeds ARE NOT CREATED EQUAL.
this is something you MUST understand.
Jack Russles are bred to kill small animals this is a natural instinct for them, is your sister prepared for that? They are also a breed that was bred to work independently fro their handler and to think for themselves, because of that they are not typicaly th easiest dogs to train.
YOu have to ask yourself What is your sister looking for in a dog?