Mrs Winifred Gillyflower was the founder of Sweetville. She was a prize-winning chemist and mechanical engineer. The Eleventh Doctor called her "nuts", and she referred to her own hands as "the wrong hands".
Mrs Gillyflower discovered a red leech and named it Mr Sweet. She symbiotically lived off Mr Sweet's nectar and used his poison to create the community of Sweetville, where the best of humanity could be sealed away once a rocket inside the empty match factory that contained the poison spread the poison across the atmosphere. Mrs Gillyflower experimented on her daughter, Ada to develop an antitoxin to the red leech poison so she could survive the explosion. She lied to Ada, telling her that she was blinded by her father. She held sermons to invite people into Sweetville.
In 1893, the Eleventh Doctor and Clara entered Sweetville to investigate the "rejects" of Mrs Gillyflower's plans whose skin had turned a bright crimson. The process failed on the Doctor, but thanks to Ada and Jenny Flint, he recovered and rescued Clara from the poison-induced stasis. The Doctor confronted Mrs Gillyflower and she revealed her plan. Clara stopped the rocket from being fired, but Mrs Gillyflower held Ada hostage and ran to the secondary firing mechanism. When the rocket was launched, Jenny and Madame Vastra had already removed the poison from it. Mrs Gillyflower threatened to shoot the Doctor and his friends anyway, but Strax shot at her, and she fell to her death. (TV: The Crimson Horror)