JWs always try to make their actions a result of something you did. Don't fall for it. You said "if I had said yes earlier maybe she wouldn't have went back." It's her choice, her actions, don't take responsibility for her bad behavior.
i know it sounds cold, but having dealt with my own family members JW craziness, I can speak from experience. JWs explain their bad behavior in terms of what you did to cause it. My sister has done awful things to her children because of "their actions", which consisted of not wanting to be a witness anymore.
People are also drawn to the witnesses because they don't have to be responsible for the state of their life. The religion takes all the decision making out of it, so the results are not the individuals responsibility.