Beverly is a recurring unicorn character in the show. One returns in The Trouble with Wendys snorting indignantly when Mavis says "last one there is a rainbow-loving unicorn". This unicorn had appeared in a previous episode when Mavis was walking through the woods.
Beverly appears in The Wrapture she shows up when Maudie tells Mavis and her friends if they make a mess she will turn them into a unicorn Beverly heard what Maudie said and she gets mad at her. Then she appears again in The Wrapture at Maudie's desk reading a magazine.
She overeats in The Mavysitters Club
Her name is revealed in Say Princess to the Dress when Mavis declares her "trusted steed", "beautiful beast", then "princess horse".