I agree with Yingying that BYB's shouldn't be supported because they make money by kind of tricking people. But I don't want you to get too scared about it.
Some BYBs are kitten mills and terrible people, churning out pets for stores and etc, it's true. But others are, honestly, naive people that want to try "cat breeding" and get in over their heads. They have solid intentions, and aren't really terrible at socializing the cats they have, they just don't know (or care) about registrationg and bettering the breed.
You can contact the breeder for a picture of her parents, or her as a kitten suckling with her mom or something, and that will tell you whether they're full-blooded. Who knows? Maybe smushfaces can have non-smushy babies!
And, if you love her, then it's already too late. She's adorable.
The only major health thing to be concerned about is PKD. Himmies can be prone to kidney problems and the biggest issue with a BYB is that she might be breeding a cat that carries the genes, meaning the kittens are all at high risk for having kidney disease. I don't want to scare you inappropriately, but you really need to contact the breeder and ask if she has records the kittens parents are PKD-negative. Barring that, there's a (relatively) inexpensive test for it here: Cat Tests
(PKD1 is the one you need).
You can submit the sample yourself or have your vet do it. Then, at the very least, you'll know if your kitten is healthy or not. PKD can't be "cured", though, but it can usually be managed.