It is interesting to note that Helen Shyres has never been portrayed accurately:
In the book, she is Sue's best friend. But is meaner to Carrie than her 2002
The 1976 version is simply a bully to Carrie and isn't Sue's best friend.
The 2002 is the most accurate portrayel. The character is mostly right for the first half, being Sue's best friend and a tormenter, but during the prom she becomes Frieda Jason and even briefly Sue Snell.
Helen does not physically appear, however, there is a character named Heather, who is a close equivalent. Though she is one of Carrie's main bullies and never attempts to help her.