I suspect this is just an excuse to get rid of her because they couldn't bring themselves to tell her her time was no longer needed or wanted. I have to do this with volunteers in my own organisation, for myriad reasons, it's not always because the volunteer has done anything wrong. It's always awkward and difficult to break it to someone that even though the organisation appreciates the time they give up and the obvious passion for the "cause", their time is no longer required. It's not quite as difficult when they have done something wrong because then you can give them a concrete reason why, but sometimes the penny doesn't drop straight away and they find it really difficult to grasp that they are essentially being told they are no longer welcome.
There are certain strictures placed upon third sector organisations that use volunteer labour by their commissioners, and we have to ensure the volunteers work within those parameters at all times. There are certain scenario I can conceive of whereby a volunteer might be expressing a point of view or an opinion that is perfectly reasonable in a normal setting, but due to the conditions of our funding would be completely inappropriate for them to air while carrying out their function as a volunteer part of the organisation, and in that case, I would have to terminate that relationship.
It does rather seem in this case that they have over-reacted massively to someone simply asking questions.