Most of surviving Church of Ireland parish records for Dublin city are on the IrishGenealogy website, but they have very few records for other Protestant denominations - Presbyterian, Methodist etc. I've seen some references to at least some of the Maddocks families in and around Dublin being Quaker which might explain the lack of findings on the usual sources, which usually focus on Catholic and Church of Ireland records.
If you think your Maddocks line may have been Quaker then the place to contact is the Society of Friends in Ireland - see : Quakers in Ireland (Irish Genealogy Toolkit)
and Religious Society of Friends in Ireland
I had a quick search for Margaret in Dublin city instead of Mary to see if anything turns up for that name instead, and while there are numerous Stokers mentioned, including two going back to to the mid 1600s, I didn't see any Margaret Jane or Margaret in the early 1800s or late 1790s. Most of the Stoker baptisms showing up in the first decade of the 1800s in Dublin city appeared to be Catholic.
They only online result I found that's even close is a baptism of a Margaret Stokes, in St. Paul's Arran quay (Catholic) in 1798. The same couple have other children listed, so the surname doesn't seem to be a transcription error for Stoker.
Where did Margaret die ? do you have a death cert for her ?
If that cert includes father's name it might help locate him in other sources, such as directories