First I will have to qualify my answers by telling you that I used this device, and it worked well for me, so I am only giving you my personal opinion here, which is a positive one. It was easy to use, and given my ability to almost fully open my mouth today (probably more than my wife would like) the results were excellent. Second, on the foundation's resources page, there is a direct link to Therabite, and I suggest that you go directly to their website where you will find a wealth of information about not only the product, but about trismus, which is the physical condition you are describing. With this and all conditions related to treatments, I offer this caveat. She/he should always defer to the opinions recommendations of their healthcare provider. I am just a patient/survivor. I would be surprized if the doctors or support staff are not familiar with this device, but if not, there is nothing wrong with the patient bringing something, whether a product or a treatment, to the doctors attention that he/she may not be aware of.
Briefly, the muscle tissues become damaged as a result of the treatments. Scar tissue forms within the tissues, and they not only lose their elasticity, but their range of motion becomes limited as well. Patients are usually warned of this process, and during treatment they are encouraged to continue stretching the muscles to reduce the problem. This may be accomplished by stacking progressively greater numbers of wooden tongue blades between the teeth, or more efficiently with Therabite's device. I can tell you that sometimes patient compliance related to staying on top of this can be difficult. When I was in the worst part of my radiation treatments, I couldn't have cared less about opening my mouth, and if my wife hadn't been encouraging me to stay on top of things, I might have a less favorable outcome today.
As to the support groups, if anyone would know about this, the Therabite folks surely will, and I again defer to their expertise and knowledge. E-mail them or give them a call, I'm confident that you will find the help and answers you need there.
If she or her husband would like to communicate with a past user, they may contact me if they like.