From whose perspective should I write this monologue in? *read the plot*?

I love the point of view. I would stick with Sarah's point. Also, after she dies, you should do a little bit of her talking when she's dead. Try like, having her go to heaven (or hell if you feel rebelious like lil' Sarah) and have her say how much she wished she had listened to her parents. Have her be like really close to her sister and write a letter to her sister from heaven saying what a bad choice Sarah made that cost her her life. Have Sarah tell...I don't know.....her sister Belle to stay out of trouble and listen to her parents. I don't know, thats what I would do. Great monologe!