In the comics:
Sarah was actually named Sherri, her name was changed for the movie, though she was much younger in the comic and aside that, played a much smaller role. She wore Shelly's engagement ring on a necklace in both the comic and movie. She later however appeared under the better known name of Sarah Mohr in the comic book adaptation of The Crow City of Angels
In the movies:
Sarah Mohr was befriended by Shelly Webster and her boyfriend Eric Draven at a young age. Sarah often spent more time with Eric and Shelly then she did at home due to her mother Darla's drug and alcohol abuse, not to mention her abusive boyfriend "Funboy". Sarah was hit hard by Eric and Shelly's murder at the hands of T-Bird, Funboy, Skank, and Tin-Tin, and was the first to learn of Eric being reborn as The Crow, when she found him in his old apartment which she still used as a home away from home.
THE CROW: CITY OF ANGELS:
A grown up Sarah, who is now a tattoo artist, befriends and falls in love with a new avatar of The Crow, Ashe Corvin, who has come back from the dead to avenge the murders of himself and his son. She helps Ashe learn what it is to be a Crow based on her experiences with Eric.
In the TV series:
Sarah appeared in every episode of The Crow Stairway to Heaven, she was Eric's closest friend in the show, and acted almost as his unwanted sidekick, putting herself in dangerous situations in an effort to help Eric out. Sarah often searches for answers for Eric in paranormal chatrooms under the screen name Skategirl.