Years back, I had a yorkie named Jess.She was beautiful and I had seen her parents, visited before we brought her home, I had seen her sibblings too and everything seemed legit and wonderful - but we had the same issue.
Her hair was super short and it just wouldent grow at all, infact, it stopped growing altogether when she was about 6 months old (and an inch and a half+ long) and she had other "defects" too, like a super long compact body, short legs, a long snout etc.As she grew, we could tell something was off, because the older she got, the more obvious those differences became.
We waited and waited and during that time we had testing done etc, but she was healthy so we just thought that her hair was growing alot slower and that she just wasnt an "up to standard" yorkie.We loved her just the same

Turned out that back in her lineage, there had been a dachshund, and the breeder had tried to "fix" her mistake by "breeding out" the mix.
Yes, she
thought she could do that.We did tons of research and kept finding other buyers of previous puppies who were having the same problems, whilst other buyers were over the moon.
If there is a mix in the lineage, it will
always find its way back into one (or more) of the pups of nearly every litter, and we happened to buy one of those pups

Yorkie parents, yorkie grandparents, but
still not 100% yorkie.
Doing research back then, we also learned than one litter of pups can have multiple studs, so whilst one pup can be purebred, its sibbling can be a mix..it depends on whose sperm was present at the time.
I also think that there seems to be a mix in her, I donīt know what it could be, but I think itīs deffinately there.I would look into it.Sheīs still super cute though!!

Adorable!
Let us know what you find out