what is the name of these series (i think)

We see a bedridden old female patient with short grey hair. There is only one person who is visiting her in her room who is her highschool friend. One day, another woman comes along to see how that patient is doing. In a later scene we see a flashback when they were young highschool students (50s probably). They were going to their prom. The woman, who visited the bedridden patient at last, threw a big rock from a bridge on top of driving car and that rock permanently injured one of those girls, who also happened to be the friend of the girl who threw the rock. The target of that rock was not the friend who got injured but another girl who was in the same car but in another seat.