My 90-year-old mother-in-law does not want to leave her house, but she is not in her right mind. What can we do?

My mother in law is 90. She has started talking to her dead husband. She will not come live with us. Her mind is almost gone. She goes out looking for him. She refuses to come live with her son and we cannot afford to put her in an assisted living home. Where can we put her in a safe place at a price we can afford, and how do we go about it. Do we need a court order to get her out of her house?