Fred,
Had a check through the Ellingham parish registers, can't find Ann, but did find a James Witt, illegitimate son of John & Elizabeth Witt of Blashford (1823 I think). Perhaps a brother ?
Had a search through Ringwood, but could only find an Ann Witt in 1804, daughter of John Witt. No other info recorded.
Perhaps this is her and she got her age wrong on all of the census returns? Maybe she thought she was younger than she really was?
Siobhán