Hair not growing back

Question
My mom & I groom her dog every spring (collie shepard mix?).  This year, her hair has not grown back AT ALL...it's the same length it was when we cut it in May.  She seems perfectly fine otherwise - no other changes at all - in behaviour, diet, demeanor, etc...any ideas?

Answer
There is a phenominom called cliiping alopecia where the hair doesn't grow back after a very short clipping but is unusual.

All I can suggest is time and patience.  Your vet might be able to discern the coat issues for you with a skin scraping.  Sometimes there are mites or allergies we can't "see".

Best of luck.

-Trish