You don't give the context for your example sentence, so I'm a little confused what it's trying to say. But it appears that the "elderly lady" did ... something ... that caused the young man to become a "dutiful son". Assuming that that's what happened ...
The writer appears to be saying that the elderly lady had some sort of plan when she did whatever it was. He's saying, though, that her plan was NOT to cause the young man to become a dutiful son, even though that is what happened. Her plan was for something else to happen. Exactly what I can't say without more context.
So the young man becoming a dutiful son is not what she planned. But that's what happened.