exterior wood door finish

I hope I have posted this in the proper forum, and if not I am sorry. It pains me to say that I need an idea for a lock or bolt for a closet door. My Father has Alzheimers disease and my Mother's bedroom closet is directly across from her Bathroom door. On more than one occasion, she has followed him going into the bedroom and mistaking the closet for the bathroom. Fortunately, she has been there every time divert him to the bathroom. But should he wake in the middle of the night, he might make quite a mess in the closet. My Mother asked me for an idea on how to keep the door locked. She does not want to change the doorknob. I suggested a chain lock or a sliding bolt lock. The molding surround the door is not flat, so adding a sliding bolt or chain bolt might be a challenge to install. Does anyone have any other suggestions on how to secure the door ? Thanks

My home is 5 years old, and many of the closets have bi fold doors on them. The problem that I have with these doors is the hardware on many of the often used doors has worn out and the door is no longer properly seated. Any suggestions on fixing this?