Rhona Austen was a splinter of Clara Oswald who was an operative of Torchwood One in the 1890s.
Having much of the same skill and gusto as the original Clara Oswald, she was one of Torchwood's best agents. She had previously worked in Edinburgh and Glasgow before being transferred to London. She sometimes spared with the Paternoster Gang, causing them some degree of conflicted emotion due to their knowing Clara Oswin Oswald.
Vastra in particular speculated that Torchwood may have been using Rhona as bait for the Doctor. Rhona herself was seemingly unaware of her origin as a splinter. (PROSE: The Paternoster's Guide to London [+]Loading...["The Paternoster's Guide to London (feature)"])