My 90-year-old mother is in excellent health, however, her short term memory is diminishing. When should she move in with me?

What are the signs I should look for to ensure my mother's safety? She has fainted in public twice with virtually no "warning". She was tested thoroughly at the hospital and her heart and carotid artery are all "clear" and healthy. I worry about her fainting at home and possibly breaking a bone or hitting her head. I also worry about her judgement and her being a target for people who might want to take advantage of her. Your advice is much appreciated!