I can see on the Internet at least two people in the last ten years who have been trying to research Mary Jane (James) Perks ancestry. They had no visible luck.
I found no evidence why she went to prison but her husband was still alive and she returned to him after serving her time. What are the options in 1891 for a woman? - probably stealing something valuable!!! Here is her life.
1861+- - Mary James born Breckonshire, probably Brecon. No Mary Jane James. 6 Mary or Mary Ann James registered in Breckonshire 1858-1864.
1880- Married JUN Qtr. Probably Brecon. Definitely Breckonshire. Husband George Perks.
1881-Census-Living at 4 Silver Street, Brecon, (St. David's Parish) with husband George Perks from Wolverhampton, Staffordshire.
1887: DEC Qtr. William Henry Perks born Breckonshire, probably Brecon.
1891-Census-Prisoner in Swansea, Glamorgan. Husband George living in Penderyn, Glamorgan. George from Wolverhampton, Staffordshire.
1901-Census-Living with her husband , Clydach Vale, Ystradyfodwg, Glamorgan. George from Smethwick, Staffordshire. William Henry living with them.
1911- Census-Living with her husband (born in Wolverhampton again) Rhondda, Glamorgan. William Henry living with them.
1913- William Henry believed to have married Florence A. Pitbryant but this is in dispute. DEC Qtr. 1913, Pontypridd, Glamorgan.
1929- JUN Qtr. Mary Jane probably died in Ystradyfodwg, Glamorgan.