The high school moved from its original site on Holywell Hill to its current location on Townsend Avenue in 1908.
Old Girls, governors and other members of the school community are invited to a dedicated service in the cathedral and Abbey Church of St Alban to commemorate the founders with current students and staff.
The extensive site includes play areas, an adventure playground, woods and an outdoor learning classroom.
The school's large playing fields include tennis courts, lacrosse pitches and a new sports pavilion.
Girls throughout the school have the opportunity to take speech and drama lessons in small groups in preparation for a variety of LAMDA examinations.