And (having now looked at the PR) Mary was shown as aged 18, and her father was a cabman - so a possible for her in 1861: Lomas Buildings, Castleton, Rochdale - RG9/3038 fo105 p17 Mary Howard aged 12, with parents Thomas (35, Cab Proprietor) and Sarah (34) - all born Rochdale. (No-one else shown in household.) Added: yes, the one I saw in 1871 was the one in Stephen Street.
I think Mary went back to using Howard for her surname and was also in jail during the census..I found a candidate for her the other day, but got called away before I could record the information for you. Also possibly found one of the "twins" in a poor house on a census.
Thanks Sue. I wouldn’t be at all surprised to find them in the workhouse - I’ll have a look tomorrow.