Complex sentence: In 1809 she opened a girls'boarding school at Grove House, Harrogate and developed it as a ladies' finishing school, a forerunner to what is now Harrogate College, but she kept it only until 1811, when she moved to London.
Split into simpler sentences: In 1809 she opened a girls' boarding school at Grove House, Harrogate, developing it as a ladies finishing school, a forerunner to what is now Harrogate College. But she kept it only until 1811, when she moved to London.