Hi Jani,
You can find material on "typical" stages of dementia in the factsheets, but no two people are quite alike, and different people progress in different ways, at different rates, with different types of symptoms. (Lot a help that is, innit?
)
One thing I've seen in my mom and heard is typical, is the dementia may proceed by fits and starts. She might go downhill pretty fast for a while, then level off and stay about the same for a while.
As to when she can't live on her own, it's generally when she's not safe any more. That will be a (probably difficult) judgement call. Most of us do stupid things (get lost driving, leave the kettle on, forget to lock the house when we leave) once in a while. One instance does not mean your mom needs full-time care. But when these kind of things get frequent, or she is driving you (or the neighbors or landlord or other relatives) crazy with panic calls, etc., it's time to do something.
Hang in there. Sometimes the early stages, when things are changing and everyone especially the patient are fighting it, can be worse than later on.
Karen