Serious hair loss on back of ear help please

My 3 year old female is in hills zd and has had hair loss for about two months now. Scrape and cultures were negative for parasites, ringworm or fungal etc is not itchy
It has not stopped, it is getting worse. Dermatologist Vet has advised to wait two months to see if it clears on its own and if not do a Biopsia. He said food allergy is unlike because is non itchy and she is on a hypoallergic diet.
What to do? Please find pics attached one is from the second of February and the other from the first of march. It is a bit worse now and hair is not regrowing.
Dermatologist said it could be stress related telegenic defluxion due to the fact that on 15 of December she had a dental extraction with complications and she was very stressed.


Thanks

Hmmm, I guess stress could do this.  Stress can do so  many things. 

I don't have any other thoughts about what it might be, but perhaps others will see this now that I have bumped it up and have some ideas.