Fewer pause at the smaller, squarer ruin set apart on raised ground to the west of the main graveyard, within its own square enclosure. This is the church known as Our Lady's or St Mary's, and what sets it apart is not only its modest scale but the possibility, noted by scholars, that it was built specifically for women or nuns, making it an unusual outlier even within this densely layered monastic landscape. It sits on level ground with views south down the Glenealo River valley and south-west towards the Lower Lake, a position that feels deliberately separate rather than incidental.

The building began as a simple single-celled nave, roughly 9.9 metres long and 6.2 metres wide, constructed from large blocks of mica schist and granite in the lower courses. The west doorway is a particularly early feature: its jambs incline slightly inward in the pre-Romanesque manner, the lintel sits above an early form of architrave on the exterior, and cut into the soffit, the underside of the lintel, is an incised saltire cross. A chancel and a north door were added in the twelfth century, extending the building eastward and altering its character considerably. The windows are round-headed with hood-mouldings; the one in the east gable carries a key pattern along its moulding that terminates in worn animal heads, a detail easy to miss if you are not looking for it. Inside the chancel, two decorated cross-slabs survive, and at the east end a subcircular bullaun stone, a boulder with a rounded, cup-like basin hollowed into its surface, rests on a rectangular pile of stones. Bullaun stones are found across early Irish ecclesiastical sites and are thought to have served ritual or practical purposes, though their precise use remains debated. The wider graveyard also holds a number of rougher crosses and cross-slabs, less refined than those inside but no less old.

The church has been partly restored and is in state care, so the fabric is relatively stable. The enclosure that surrounds it distinguishes it physically from the main monastic complex nearby, and that boundary, however low and worn, is worth registering as you approach. The animal heads on the east window hood-moulding and the saltire on the door soffit reward close inspection; both are the kind of detail that reads as blank stone from a distance.