Locked? Unlocked?

My Mother has lived in this house for 16 years.  Our front door has a deadbolt that is engaged when in the horizontal position.  There have been some days that I noticed the deadbolt unlocked; in a vertical position.  On one such occasion I asked my Mother if she was expecting someone.  She said "no why?".   I told her that the front door was unlocked.  She had gotten the newspaper from the front porch and left the door unlocked.  I dismissed it, thinking she just forgot.  The next time I noticed it and asked why the door was unlocked, she said it wasn't unlocked.  That the door lock has always been in a vertical position.  She was convinced that I was wrong and turning the deadbolt the wrong direction.  It is like she has created a new memory of how the lock works.

I now do a walk through each night after she goes to bed.  I make sure all doors are secured and properly locked.  I have found the door to the garage door ajar and the front door unlocked once or twice.  It is not a regular thing, but I regularly check the doors every night to be sure we are secure.