Hello & welcome...Has she always had the protrusion or did it suddenly come up? If this is recent, she needs to be xrayed for a Tumor....
Also, An Inner Ear Infection can cause what your describing........They are sometimes hard to diagnose because the infection is so deep.....There is a new instrument that can diagnose them fairly easy now, but most Vets don't have it......If blood work showed an Infection somewhere (White blood cell count), then I'd be looking at that.....Did she get any better on Antibiotics.....For Inner Ear, combination antibiotics are used to break the blood/bone barrier and actually reach the deep seeded infection....They have to be given for quite a few weeks...
Medications for nausea are usually given for Vertigo or Vestibular Disease....These do help the dog feel much better....It's my understanding that Vestibular Disease will run it's course in about 6 wks......It may be different, now...
Hope you get this figured out....Let us know with updates......Good luck, Karla
Is she and older dog by any chance....? If she is, I would have the vet check her out for vestibular disease....this disease will affect a dogs equilibrium. It will typically affect older dogs. I really don't know much about it, but a friend of mine had a dog who was diagnosed with this disease...so...it's just a thought.
Here is some info I found on Vertigo and possible causes...along with the website......
Vertigo can have an endless variety of causes. Most often, vertigo in dogs is contributed to indigestion or liver problems. Overeating or being malnourished can result in vertigo in some cases. Hazardous chemicals or other products of the dog's environment can trigger vertigo episodes. The condition causing vertigo can be as severe as a major neurological problem, such as a tumor, and as mild as an overly tight collar reducing a dog's air supply.
Read more: Vertigo in Dogs | eHow.com http://www.ehow.com/about_5502857_vertigo-dogs.html#ixzz1fidJDvqU
Basically it seems that you really just need to find the cause...
I wish I could be of more help....maybe other members will be more knowledgeable in this subject.
Best wishes to you and your dog....Connie