My mother who has Parkinson's, is diabetic and onset of dementia will scream from her dreams at night, should I wake her?

Not sure about waking her, but her sleep symptoms should be mentioned to the doctor (perhaps you've already done this). A variety of things can cause sleep disturbances, for example, side effects from certain Parkinson's medications. On the other hand, something as simple as a UTI could be involved. Best wishes to you and Mom.

Person's with Parkinson's have a protein deposit in their brains called Lewy bodies (after the researcher who discovered them a hundred years ago). When they develop dementia it is often of the Dementia with Lewy Bodies variety. And that, in turn, is closely associated with a sleep disorder called RBD (REM Behavior Disorder). My husband had RBD for many years before the dementia came on. In it he acted out his dreams. That is, if he were running in his dream his legs would be pumping in the bed. Once he swung his arm so hard to hit the bad guy he threw himself out of bed. Talking and yelling were sometimes part of this.

The good news is that if that is what your mother is experiencing it is highly treatable with clonazepam.

Wake her up (carefully -- don't get in the way of a swinging arm!) and assure her she was only dreaming and she is safe at home, etc. Ask her if she remembers what she was dreaming about. Try to keep a journal for a while, then discuss her night symptoms with her doctor.

If this is a sleep disorder, it is not psychological. She is not doing it for more attention or to strike out at you or because she feels abused or neglected or any such reason. It is about brain chemistry.

I hope that you and she can both get some relief.