Valerie, this could be old Catherine Taggart, from Brian's burial index:

TAGGART, Catharine 98 Mal 18 Nov 1846

So she was born (possibly Catherine Killey), in 1748.

Is Thomas Taggart b 1826 your direct ancestor, and is the "lead miner" information from what you already knew, eg as the father on one of his children's marriage certificates, or from the "nephew in 1851 census"?

Jean