For twenty-one years Whittle worked for
Cadw, the Welsh historic environment agency as their Inspector of Historic Parks, Gardens and Landscapes. She retired in 2014. She is a former president of the
Welsh Historic Gardens Trust and is a trustee of the
National Botanic Garden of Wales. Whittle, the holder of a
Master of Arts degree and a fellow of the
Society of Antiquaries of London, lived in
Usk,
Monmouthshire for many years, Following her relocation, Whittle took on the chair of the Cambridgeshire Gardens Trust. Whittle was a member of the
Garden History Society from the early 1980s and between 1989 and 1997 co-edited, with Jane Crawley, their journal
Garden History. She has a particular interest in Tudor and Stuart gardens. In 1991 she re-created the 15th-century garden of
Sir Roger Vaughan at
Tretower Court in
Powys, Wales. She also discovered evidence of the 17th-century appearance of the gardens at
Raglan Castle, now destroyed, which has been published in the
Cadw guidebook. In 1994 Whittle led work on the compilation of the
Cadw/ICOMOS Register of Parks and Gardens of Special Historic Interest in Wales to assist owners, developers and planners to manage the country's landscape heritage. She became a trustee of the
Hobson's Conduit Trust in 2018 and vice-chair in 2020.
John Newman, author of the
Gwent/Monmouthshire volume in the
Pevsner Buildings of Wales series, recorded his debt to Whittle in the foreword to his work. ==Selected works==