You're a treasure, Ursula. Thank you so much for that marriage info. I'm rather amazed at the convoluted research path you describe but in a way I'm not surprised, as the entire family was pretty interesting.
Thought you'd like to know that in 2007 I published a book on the Pierssené/Fatt connection - Pierssené, a Huguenot Family of London - and on page 150 I explain Stephen Fatt's name change. Basically, in 1827 he married Sarah twice in two weeks - the first time as Fatt, the second time as Flockton. Because some of the Fatts later adopted the name Pierssené, the book also contains a great deal of info about the Fatts back to William Fatt, c 1690-1773, and some info about the Schmacks. In hindsight, it makes sense to me that Thomasine Flockton married her second husband in Prussia, as the Schmacks were German.
To answer your specific question, Sarah Flockton was the daughter of Rev Jonathan Flockton and his wife Hannah Cole, who were married at St James Piccadilly on 19 January 1792. Sarah was their fourth child, baptised on 12 March 1799 at Hambledon, Surrey. I've found 12 siblings for her, and she herself had 10 children. I've researched the lives of the Flocktons back to the year dot and have a well-developed draft book waiting to see the light of day. You have now filled one of the gaps holding up the finalisation of that book. Next year I'll be publishing a book specifically about Sarah's granddaughter, the botanical artist Margaret Flockton.
Best wishes
Louise Wilson