Hi Timetraveller,
Is your Ann Lewis the one born 4th qtr 1852 registered Cheltenham vol 6a page 356?
Age is about right and it seems to be the only one for Cheltenham around that time.
As you say, she says she was born in Cheltenham on the 1891 and 1901 censuses although 1881 is Gloucester.
The only Ann Lewis that I can see in Cheltenham, has the parents Jeremiah Lewis born 1822 and his wife Caroline 1825 Cheltenham.
Jeremiah died in 1869 so he would have been deceased when Ann got married.
I though there would have been quite a few Ann Lewis in Chletenham as it is not an uncommon name.
You have quite a problem to sort there I think.
Best of luck,
Elizabeth