Birdbrain (don't like calling you this) there are many Laggans but only one parish of Laggan, SW of Newtonmore. The website is http://www.laggan.com/
Aberarder is at the NE end of Loch Laggan, the old roofless church is beside Aberarder House. The small crofting community of Crathie were mostly RCs and used this as a burial ground. The last inhabited croft was abandoned after a housefire when the Spey dam was being built, this construction flooded their land beside the Spey. The chapel , built for them by MacNab of Dalchully, was taken down at the same time. It was below Dun Da Lamh, south of the dam. The folk weren't particularly devout apparently, if there was no priest coming on a Sunday they would just toddle along to the Free Church. You might try the Heritage Group for a list of the gravestone inscriptions. For an overview of the district try
http://wheresthepath.googlepages.com/wheresthepath.htm
Type in Laggan, a few come up, try the third, using the compass on the map on the left page, the aerial photo follows on the right. Skoosh.