SOLVED. revenge thriller; After graduation a girl is raped / traumatised on a train by a group of schoolboys. Later in life her sister befriends..... [s]

[Rich]

After graduation a girl is raped / traumatised on a train by a group of schoolboys. Later in life her sister befriends and murders them one by one

[Lobstergirl, au gratin]

Rich, are you still looking for this or did you find it?

[Lobstergirl, au gratin]

No response but this is likely The Disappearance Of Lyndsey Barratt

Kirkus says: "Hours after stellar student Lyndsey Barratt suffers the humiliation of receiving her drama-school diploma in the absence of her parents (her ineffectual father, who couldn't bear to be seen in public with her wheelchair-bound mother, begged off), she's suffering the torments of hell. The cricket team from nearby Winstanton School, flushed with their latest victory, has taken offense at her entrance to the railroad car they're occupying and has retaliated by raping and beating her."

"Lyndsey, shepherded by her twin sister Linda, disappears from Hope Green Hospital...."