Assistance with Cervical Dystonia / Torticollis
There are several conditions that produce similar signs and symptoms. Some are permanent, others are not. Based on what has been shared so far, I am assuming that this client has the permanent condition. At it's root, this problem arises from a central nervous system "disturbance".
Botox essentially deadens some of the nerves to block transmission of the signals for involuntary muscle contraction. At the moment, this may be the single most effective therapy, though it does not address the source of the problem. Without ongoing injections, the client's problem will return.
You can't "deep tissue" or ""trigger point" this problem away. With those methods, the best you can hope for is some measure of temporary relief. Do what you can.
I don't currenty have a client with this problem, but I would enjoy having the opportunity to work with it. Over the past few years, I have been studying the neurology of stuff like this, and neuro-based forms of manual therapy including dermoneuromodulation, positional release, and active methods like muscle energy technique and active isolated stretching. (Feldenkrais looks interesting, but haven't studied it yet.) My intention would be to use neuro-based work to disrupt the signals for involuntary contracture, and hopefully (over time) eliminate the source of the problem. I don't know if this is actually possible, but I haven't yet seen anything that tells me not to try.
If you are not familiar with neurological concepts and how to apply them in your work, the best thing you can do for this client is refer them to a physical therapist that works with neurological dysfunctions.