omg I love the little sister, and how much the older sister loves her.
I wonder if in the book there was a misunderstanding between Dylan and the ML. It seems weird that she would automatically be a villain and covet her sister's husband, even after the point of being married to another man. I get the feeling that she was trying to keep her younger sister away from him as much as possible by any means necessary, and being desperate at the funeral might mean her trying to get on his good side so she can stay in contact/take care of her sisters child that was left behind.
I just don't see how someone who originally loved her sister so much she would wake up in the middle of the night to check if her younger sister was still breathing would immediately flip a shit and go boy crazy.