NaeNae, I have no doubt that your SIL is one of the few breeders suplying pet shops who do treat their bredding dogs well but TBH I don't understand how someone who loves their puppies can sell them to a pet shop where anyone with the right amount of money can just walk in and walk out with the puppy 5 minutes later. Many of the young dogs that end up in shelters are impulse buys and IMO you shouldn't be able to buy a pet on impulse.
Some pure breeds are expensive, there's no doubting that, but the cost of a pet-shop puppy and a pure breed puppy from a breeder isn't much differant. Years ago when my Dad had problems with a pure breed b!tch he bought as a work dog (too much 'eye')we went back to the breeder and he took her back to breed with other dogs that didn't have enough 'eye'. Had she come from a pet shop our only option would have been trying to rehome her (not easy if you have a useless working dog) or putting her down.
A puppy from a reputable breeder comes with all its vet work done, microchipped, wormed and socialised. All these things take time and money. Just using Labs as an example because that is the breed you mentioned, conscientious breeders have their dogs X-rayed for hip dysplasia and osteochondrosis, and have their dog's eyes tested annually by a veterinary ophthalmologist to detect any disease at the earliest stages, and do not breed from affected animals. All these tests are expensive but by doing them breeders make sure that these issues are not passed on. If one of their buyers contact them to say that the dog they bought has developed these issues most breeders will take this into account and won't repeat the cross. Many breeders will also offer to find a solution that leaves all parties happy. If one of the labs that your SIL sells to a pet shop has congenital issues she won't even know about it so she can't do anything to stop it happening again.
The overabundance of puppies in pounds and rescue organisations means that pet ownership is not unaffordable to anyone. TBH, I know this sounds harsh, but if a person can't afford the upfront costs of getting a dog then maybe they should ask themselves if they can afford the ongoing costs.

ETA - I saw a some gorgeous labs in the pound last week (including a young boy less than a year old) so if anyone wants a lab they can pick one up for a fraction of the cost at the pound if they're prepared to wait until one is impounded or surrendered. Also Staffies, Lhassa Apsoos Maltese, Poms, a ****er Spaniel..... If it's a pure bred you want the pound has them.