Rootschatter Barbara_F has kindly found a non-conformist baptism for:
15 April 1764 - Rebekah, daughter of John Hartley, mercer, Fleet Street.
My Rebecca's youngest child (Thomas Mark Larcher) was born 15 Jan 1820. On the Protestant Dissenters Register Andrew Larcher marks, but Rebecca signs Rebeker Larcher. Her father is named as John Hartly, weaver.
For the two to be the same person, John would have to have changed occupation from mercer (textile merchant) to weaver, and Rebecca would have been (at least) nearly 56 when Thomas was born. However, Fleet Street is less than 3 miles from where the Larchers lived.
My gut feeling is that they are different Rebeccas, but is there a link?
Philip