I've had clients who took a similar "high road" approach with difficult people in their lives. For example, Yvette stayed politely silent when a coworker, Fred, brazenly stole her ideas. Janae cleaned up pizza boxes and drinking glasses left by her college-age daughter, Emily, as uncomplainingly as she'd once changed Emily's dirty diapers. And Cynthia and Rob's romance was based on lots of give and take: Cynthia gave—back rubs, compliments, gifts—and Rob took full advantage without ever reciprocating.
All these women were as long-suffering as Tina Madden, and the people around them responded just as Nu Nu did: by exploiting the living hell out of them.
The problem is that trying to change unfair behavior with submissive niceness is like trying to smother a fire with gunpowder. It isn't the high road; it's the grim, well-trod path that leads from aggressive to passive, through long, horrible stretches of passive-aggressive. The real high road requires something quite different: the courage to know and follow your own truth. If anyone in your life is exploiting your courtesy and goodwill, it's time you learned how all of this works.
Next: How to tell where your relationships are going