Well that's what I thought, too Phoenix. There's no trace of Rebecca in London after the Settlement Exam, but there is a Yeovil burial of a Rebecca Underhay in 1815 which I believe is on FMP. She would be about the right age but I don't know how to prove it one way or the other! There is also a burial for a Maria Underhays in 1810 in Yeovil but it doesn't give an age
However one of her daughters, Mary, was married in London in 1818 and another daughter Martha was married in London in 1838. Mary was 14 at the time of the Settlement Exam and Martha about 8yrs old. Would they have been left in London if Rebecca was shipped off to Yeovil? Or perhaps they went with her and came back later. Again I don't know how to find out apart from a long visit to Somerset Archives!