Oh, Heavens no!!! I would never go to a physical therapist or chiropractor for an AAI pup! She does need testing (most likely an MRI) done to see what is going on. Yes, AAI can be diagnosed by xray, but it is possible that other things are going on. Sammy, my little foster, is a perfect example of what can be there that you don't see.
I don't mean to be rude at all, but my concern is that your holistic vets have overlooked neurological deficits in your pup all of these years and that would really bother me. If they were unable to diagnose it, how do you think they will best know how to handle it now? Maybe they would suggest surgery....but maybe not....the ONLY way to know what is going on with Cassie is to get that testing done. It is expensive, yes, but better than playing guessing games and going to someone who could end up paralyzing or worst yet killing her. One wrong move of her neck and those things could very well happen. This is a very serious condition...don't let the fact that she has lived with it for five years lull you into believing it is not serious!!
Get to a neurologist and get a FIRM diagnosis. You do not even know for sure that she has hydrocephalus. I am going to try to get a video of Sammy in the next day or two to show you how he walks. People are stunned when they see the laundry list of things that are wrong with him....he still gets around but he is indeed a really messed up pup and there is no way I would allow someone to mess with his neck and try to strengthen his muscles...that wording is scary!!
Here is a link about Sammy and his problems:
http://www.yorkietalk.com/forums/sic...ro-issues.html