Rather than lying flat over a grave as intended, it had been repurposed at some point as a plinth or prayer step, built into the base of a later tomb. Only 86 centimetres long, it is easy to overlook, and for a considerable time it went unrecorded. The slab is made from fossiliferous limestone, a stone threaded through with the remains of ancient marine organisms, common in the Kilkenny area and widely used for medieval funerary carving.

The slab came to light during excavations at St Mary's carried out by Cóilín Ó Drisceoil in 2019. Across its surface, cut in incised Lombardic script, a style of lettering used widely in medieval Europe and found on many Irish grave monuments from the thirteenth to fifteenth centuries, runs a Latin inscription: HIC IACET ISABLLA LÃG HÃ. This translates as "Here lies Isabella Lanigan", though the surname abbreviation leaves some uncertainty, indicated by the question mark scholars attach to the reading. Beyond the name, nothing else is recorded about Isabella. She is a person reduced to a few letters on a repurposed stone, her original burial place unknown, her dates unrecorded, her family history unverifiable from what survives. The abbreviation of her surname is a reminder of how medieval masons economised on effort and stone, compressing familiar local names into forms that made sense to contemporaries but can puzzle later readers.