Katie Collins is the male protagonist's high school crush from Silent Hill: Book of Memories; however she ended up dating a fellow student named Trent Baker. Her brother is Matthew Collins. She is the Wood Guardian (Matthew is the Wood Guardian if the protagonist is female).
During the events of Silent Hill: Book of Memories, the protagonist was able to change history so that Katie dumped Trent and instead formed a relationship with the protagonist.
Katie was in a relationship with Trent Baker, who was madly in love with her.
In the blood scenario, difficulties were brought on because Trent was unable to get along with Katie's friends, causing tension between the two.