She started from last year asking me how to write a check mind you she's 70 but shes very crafty and I've shown her to go to her phone to find out info but lately asked me where is the button to turn phone on & off. She's great at most things then has lapses & now her sleep pattern is one night no sleep and the next day sleeps for 10 hours. What phase of dementia is she and can she go downhill quickly or she can decline super slowly lasting 5 10 20 years?
I don't think anyone really knows, so many factors that could shorten her life or increase her years.
From your description she is at the beginning of her journey. If she has sudden symptoms or increased symptoms you should have her checked for UTI. Those can take on dementia like symptoms.
Now is the time to have a discussion about what she wants for life sustaining measures, set up POAs and do a will. I am sorry your family is going through this disease.