Complex sentence: She was the first to use the term "Green Belt" for the protected rural areas surrounding London including three hills in Kent (Mariners Hill, Toys Hill and Ide Hill) which she helped to protect from development form part of the belt.
Split into simpler sentences: She was the first to use the term "Green Belt" for the protected rural areas surrounding London. Three hills in Kent (Mariners Hill, Toys Hill and Ide Hill) which she helped to protect from development form part of the belt.