Is it wise to obtain a physician's certification now, before she moves in, that my mother cannot live alone, requires assistance with activities of daily living, and would otherwise require more expensive housing/care if not paying me? Will this help to preserve option to apply for Medicaid in the future? Currently does not qualify but already diagnosed with dementia.
Get all the paperwork you need in order.
POA, Trusts, Know where all the paperwork is. The Elder Care Attorney can also help with paperwork for Medicaid.
You may have to become her Guardian but if all the proper steps are taken you might be able to avoid that. And avoid it if you possibly can.
After you have done that then I would get a "formal" diagnosis.
Sounds backwards but there may be a slight possibility that if you have paperwork giving a "dementia" diagnosis prior to getting trusts and all the other paperwork someone may say after that she was not competent at the time the documents were drawn up. (paranoid maybe but you never know)
The attorney can draw up a type of "contract" or "budget" that would permit you to charge your Mom for food, housing, portions of telephone, cable, gas, electric. As well as your Housekeeping services and travel. Not to mention actual "Care-giving, bating, dressing and any other aspects of ADL's. As she declines you could increase your "fee" or add an outside caregiver. I strongly suggest that you get another Caregiver as you can not nor should you do this alone.
At some point you need to be a Daughter more than you need to be a Caregiver.
And if she has any health problems get an assessment from Hospice sooner rather than later. Take full advantage of the services that Hospice can offer as well as all the equipment and daily supplies and extra help that you can get.