Mom put my fingers in her mouth last night, like a baby would do. Is this common?

I'm not that familiar with Lewy Body/Parkinsons related dementia. I am sorry to hear of your mother's progression. I have read that once the patient is in the final stages of dementia, they seem to be quite similar. I know it's tough. Is your mother on Hospice?

My LO has Vascular dementia with possible AD too. Her doctor diagnosed her with Profound Dementia over a year ago and she's progressed substantially since then. He described it as her mind returning to infancy, so that she has the mental ability of a young child or infant. At one time, she would call out, mama, daddy, but, that stopped and she is no longer verbal. She seems to be in a pre-verbal phase now. I'm not sure what to expect from here.

Does your mother seem to be awake or is she mainly sleeping?

Just days before Dad passed with Parkinson's, maybe a bit longer, he did a sort of 'fake eating' where he would reach out into the air and bring imaginary food to his mouth, then chew. If I remember correctly, most of the time his eyes were closed then, though he was in an upright position in his wheelchair.