After listening to Renee's story, Arabella asked the former what she planned to do. And Renee said she would resign as Arabella's maid.
It was so she could move freely, and Arabella won't be implicated in her future actions. Renee was thought full enough to think about that.
But Renee was furious and hurt that she wanted to kill Chester and Fatima. She said she would poison them or do whatever it takes in any way she could just to ensure they get a taste of suffering too and end up dying painfully just like the way she did as Evelyn.
Renee's hatred for Chester was rekindled after seeing him again. Rather, it was only buried deep inside her heart. The embers were fully alive all this time and were just waiting to be set ablaze.
Fatima was a different case though. Renee died thinking Fatima was her friend. Thus, after calming down a bit, Renee thought she would try to verify first if Fatima was truly in cahoots with Chester.