Hi,
I did check the parish registers for Inglesham and Highworth, but unfortunately, Florence wasn't christened in either.
As you know Jesse Ball was listed as her father, I think you're probably right about the marriage cert. for Jesse and Edith, and at leasst we know that Edith did have an illegitimate female child which I suspect is probably Florence.
The bastardy records show that William Iles was the reputed father, and there is a DOB for the child. If the Florence Ellen Boulton registered in the highworth district has the same DOB, and Edith is the mother, then I guess it would solve the mystery.
If I can help at all with your quest, please feel free to ask.
Good luck, and would love to know the outcome in the future.
Paula