I'm not sure that you have to mention that she has passed away, but if you do and need a single adjective, I would use "late" -- to my late mother. But perhaps a nicer approach is to say she is "missed" or "remembered."
To my mother Mary, whom I remember for her kindness.
To my father John, whom I respect for his honor.
To my father who taught me honor.
To my mother who taught me kindness
and whose influence is missed by us both.