Hi Guest
The only thing I could suggest is that maybe it is hormonal and could be due to her coming into Season

My friends Staffie bitch had a litter of puppies on the 29 October she held on to her coat very well until the last couple of weeks, and now she looks bald in some places. It is more noticeable when the light is shining on it, but I would never of thought she could have lost coat as they don't really seem to have that much to start with :D
Hopefully this is the cause of her hair loss.
It might be worth contacting your breeder as well though just to see if she has ever heard of it before.
Best wishes
Derryn