The only thing she needs is to forget him and pray.. that helps to heal her wounds over that guy. It could take months or two or depend on your friend, if her holding him too long the more months will take to let him go.
Just talk to her everyday in some funny conversation,tell a funny story you know, make her laugh more often on some silly jokes. Enggaged her in keeping busy not staying in her room, join something like a aerobics on a gym , buy some good novel pocketbooks or just ask her to stroll along with you in a mall or some intersting places here.
Sometimes love can be deceiving it just happen that cheater knows how to end his ways or exit in undetect manner.