Mabel married William SHARMAN (-CRAWFORD) at Bangor, Co Down on 5th December 1805 and bore him eleven children.

She was heiress to her father's estates of Crawfordsburn and Rademon in Co Down as the result of the death of her brother Arthur Johnston CRAWFORD, who, in a pact with his father John, broke the entail in favour of Mabel. (The estates would otherwise have gone to John's brother Captain Arthur CRAWFORD or his son James.) For more details of this arrangement see William SHARMAN-CRAWFORD.

Mabel was buried in the family vault at Kilmore and a portrait of her was at Crawfordsburn House, although its present location is unknown.