What is required to have a person declared incompetent?

Mom's dementia is soon going to put us in a position where we will have to forceably move her from independent living to assisted living. She refuses to go. We are already doing cleaning, laundry, finances, shopping, monitoring her health, etc. She can't work the appliances, or remember what she did five minutes ago, can't take medicine, cashes checks, hides the money or loses it, cashes more, almost deaf, incontinent from laxative abuse which we can't stop wears the same filthy clothes every day, hasn't bathed in six months. But she can still get up and dress herself, answer simple questions (lies a lot), make her bed, go to her hair appointment, get herself to the restaurant to eat (anorexic - most of it goes in her purse) The doctor said she "isn't there yet". Her confusion, laxative abuse, lack of ability to maintain her hearing aids, not remembering what she has done or has been said for five minutes, not washing or bathing along with bowel and bladder incontinence is making her a danger to herself. She refuses to use the elevator and walks up a steep flight of stairs to the hair salon. She is beyond the point of listening or remembering, weak, depressed and horribly negative. She needs more oversite and we can't help her when she is living in a facility where independent living means they have no control over residents personal behavior even if it is life threatening.
What does it take to declare someone incompetent so that a decision can be made to move her without her fighting back? We have POA and health care proxy, but if she is legally competent, can she still file legal papers to stop it, change her will, keep us from seeing her etc? I doubt she would as she is unable to plan five minutes ahead, but you never know. Her dementia is advanced enough that she is in complete denial about what she does and doesn't do because she can't remember much of anything so she lies and says what she thinks it should be. For example, the other day she nearly lost her bowels in the restaurant. I was notified by a resident. When I called her she was all upset, sure she was sick. We know it is from overdosing on laxatives. The next morning she denied she ever had the problem and said she had been constipated for four days and we were lying about what happened. Isn't this a sign she is incompetent? We just want to help her and move her somewhere safe because we can't be there all the time to stop her from her self destructive and dangerous behavior.