After her husband's death in 1722, Lady Mary moved to Abney House full-time, becoming the first Lady of the Manor of Stoke Newington in her own right. She was said to be helped in designing the landscaping of the grounds as an English garden by the learned Dr Isaac Watts, who had been a long-term house guest of her and her late husband, and continued to live in her household. The neighbouring Hartopp family of Fleetwood House, who leased the eastern part of the park to Lady Mary, also helped with the park.