Does Mom have dementia, or is she just lazy?

Mom is 73. Since my father passed almost 20 years ago, she's lived with either 'men' or family members. Her entire life with my father, she never had to lift a finger. He cooked and taught us (5 kids) how to cook. We also cleaned and did the laundry from the time we could reach the sink with a chair. She spent her life very leisurely and has never been the loving 'Mom' we should all have. Just very selfish, domineering, and critical.

She's been living with me for 6 months. When she isn't sleeping (which is a lot), she's either watching TV, eating or smoking. That's it. She leaves dirty dishes and wrappers all over the house. She doesn't clean her own room or bathroom. If she does happen to put a dish in the sink (rare) she'll pour stuff like cereal in the sink and not rinse it out. She opens cans and leaves them on the counter top and makes a big mess and leaves it for me to clean up. She doesn't do her laundry either.

When I try to converse with her, she says "Oh well" or "Whatever". My siblings say that means she has dementia, but she's never had any interest in her children. Never. When each of her children moved away from home she never called to ask how we were. When we would call her, she didn't ask us any questions. She acts pretty much the same as she's always been, uninterested in anyone except herself.

When it's just me and her, she makes all these noises like she's in so much pain she just can't do anything. The noises increase while I'm cleaning. But, when anyone comes over, she doesn't make noises and seems fine.

She also refuses to go to any type of doctor (eye, ear, GI). I just don't know what to do. I've asked her to do simple things like unload the dishwasher, etc. She says she can't.