Based on your username, can you speak spanish? I think I can explain better in spanish, but if not, I hope you don't mind if I use a translator.
Lunes a viernes por la tarde en la entrada de la escuela, el balón de volleyball puede activar 2 eventos, uno con Elena y otro con Angélica, no sé si sigue un patrón o es completamente aleatorio, pero prueba por 2 semanas (tiempo del juego).
From Monday to Friday afternoons at the school entrance, the volleyball can trigger two events, one with Elena and one with Angelica. I don't know if it follows a pattern or is completely random, but try it for two weeks (game time).