D..
If she has dementia, it shouldn't matter if she is doing this "on purpose" or not. ("On purpose" is a really relative term when there is dementia involved. Strange noises from dementia patients' throats, which sound like Tourette's might be "on purpose" too, but it doesn't matter. It's part and parcel of having the dementia.)
First, seizures need to be ruled out by the neurologist. I will bet that he will find abnormal activity in her brain waves when he does a brain scan. I don't know if he can attribute the abnormality to seizures unless she has one while he's doing the test. If seiziures are ruled out, then it's just part of the dementia.
I'm sorry you are going through this. It's a very hard road, JC, mostly for the family and caregivers.
Dawn