I'd say as long as she's only selling them for a reasonable adoption fee then go for it. I would never buy a "designer dog" from someone who breeds them intentionally but I know accidents happen
And these puppies deserve a good home. Mixes are wonderful pets too. Who knows how they'll turn out so far as looks or if they'll be shedding, low shedding, or non-shedding. As long as you like chihuahuas and yorkies then you should like however the mix turns out. Hopefully this breeder will place these pups with a spay/neuter contract and use any money she makes to spay and neuter the mother and father!
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~Magnifique Yorkies~
Purchasing from backyard breeders, pet shops, and puppymills perpetuates the suffering of other dogs.
Educate yourself and buy from reputable breeders or rescue.