Ar ôl graddio ym 1973, gweithiodd Margaret yn y GIG yng Nghymru o 1974 nes iddi ymddeol yn 2010. Fel Prif Weithredwr y GIG am 14 mlynedd, arweiniodd ar uno nifer o sefydliadau, gan gynnwys sefydlu Bwrdd Iechyd Cwm Taf yn 2008.
Graduating in 1973, Margaret worked in the NHS in Wales from 1974 until her retirement in 2010. As an NHS Chief Executive for 14 years, she led the mergers of a number of organisations including the establishment of the Cwm Taf Heath Board in 2008.