She worked alongside other feminist advocates such as Patricia Brennan and co-founded the journal Women-Church[4] with former Catholic nun Erin White.

"Watching Ms Marsh, vested as a priest, join the procession to the altar", O'Reilly said "it strongly came to me, it really is OK to be a woman"'[8] As a member of the Melbourne synod she played a leading role on the committee on women in the episcopate.

She has been a member of various church bodies in the Anglican Diocese of Melbourne as well as nationally and internationally, including Chaplain, General Synod Standing Committee 2007 to 2014.

On 17 September 2023, the Movement for the Ordination of Women (MOW) held its 40th-anniversary celebrations at Christ Church St Laurence, Sydney.

After the church service at which Kay Goldsworthy preached, O'Reilly gave the Dr Patricia Brennan AM Lecture, in honour of the founding National President of MOW.