Her breakthrough came in 2001 with her role in the Johnny Vaughan vehicle 'Orrible. She was later chosen to play Gwen, a young woman who would later become Queen Guinevere, in the BBC One fantasy TV series Merlin. In an interview, Coulby stated that she enjoys being able to play the character from Gwen the humble, lowly maidservant all the way to Queen Guinevere of Camelot. In that capacity, she starred in all the five seasons, and most of the episodes, right up to the final one.
Queen Guinevere
Gwen