This thought had occurred to me as well, Shestu. The fact that a great many Sheelas are to be found over (or near to) the entrances into churches is very suggestive to me. The Linkirk Faery Holes (below, under Faeries) have a very vaginal entrance, and I have often wondered if they have been carved at some stage to intentionally give this effect. Unfortunately I cannot say for sure, since they are completely flooded in the winter months and the force of the water has no doubt been doing some sculpting of its own.