That's it. That's right - "in HER life".
This is Riona's life, and she, and only she, is responsible for what factors take place in her life.
I repeat, she could have stopped communicating and doing business with Quinn at any moment, but she didn't.
The truth is very simple - everyone is responsible for their own life, and for the troubles that sometimes arise in this life.
And no need to blame others.
You are right about one thing: everyone is responsible for their own lives. Riona could have walked away, she could have probably said "no" - but she didn't. However, that doesn't change the fact that Quinn is not a neutral observer, but an active manipulator who deliberately made this choice difficult for her.
Yes, she is responsible, but that doesn't mean her role can be erased. If everything was so simple "just walk away, just refuse", then there would be no manipulators and abusers in the world. People get stuck in difficult relationships, addictions and patterns not because they are stupid, weak or feeble, but because that is how manipulation works: it gradually narrows your options, distorts your perceptions and replaces your interests with its own.
So yes, Riona is responsible for her decisions. But that doesn't make Quinn innocent, she "used" her, and that is a fact. You can simultaneously admit your responsibility and her manipulation. The world is not black and white.