Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today.
I am sorry to hear that Emily has been suffering with vestibular disease. As I am sure you can appreciate based on the variety of treatments she has had, this is a condition that can be triggered by a range of issues. Most often it is associated with middle ear infections, head trauma, brain based infections, and tumors of the middle ear or brain stem. And I must warn that her age and lack of response to treatment thus far, cancerous growths would have to be considered here.
Now you have not mentioned how long she has had these signs or how long the anitbiotic treatment course lasted, but I would note that often middle ear infections (and some brain infections) will require long courses (ie 4-6wks) of treatment to settle their signs. That said, if she didn't respond to the course of antibiotics she was on, then we have to consider that either that the bacteria present were either not sensitive to that drug, resistant to it, or that this is not being caused by a treatable bacterial infection.
Therefore, at this stage, you may wish to speak to your vet about having an x-ray or MRI scan of her head. An MRI would be ideal since they'd let us see her middle ear and into her brain (to appreciate growths or density changes suggestive of infection/inflammation) but often cost prohibitive. Still while x-rays won't let you see into her brain, the will allow you to appreciate her middle ear/bullae. And this can tell you if there is middle ear involvement here (and sometimes we can see growths or changes to tell us which agent is causing mischief in the middle ear). At the same time, if middle ear infection with a resistant bacterium is suspected, the vet can take a sample from the middle ear for bacterial culture. That way if middle ear bacterial infection were to blame, you'd have an answer to what antibiotic it was vulnerable to.
Otherwise, if you didn't want to have Emily undergo advanced diagnostics like these at her age, then broad spectrum treatment would be indicated (which is what you have listed as being tried already). If she doesn't respond to these, then we can only really try another antibiotic (in hopes that if bacteria are to blame, then it'd be one they were sensitive to) or assume that a nasty tumor is present and just aim to keep her comfortable while she is with us.
Overall, Emily is an elderly lass and her failure to respond to treatment does raise concerns that her signs may be due to something that cannot be cured. Therefore, without further testing to pinpoint the cause of her signs and see if it is something treatable, we cannot predict whether she will ever fully recover. And with her lack of treatment response to the range of agents you have used already, I must say that it is quite possible that this head tilt is here to stay and full recovery would be less likely. That said, as long as she is otherwise happy, eating, and doing the things she enjoys, then there is no reason to not keep her comfortable and enjoy your time with her.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,
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