There is now a port of refinemesh() available for PDEModel. Like refinemesh(), it works for 2D linear triangular geometries only.
This is likely how would run your problem:
create your model as a pde model
proceed with your geometry definitions.
When you get to meshing, you instantiate your mesh as usuall, but then can refine the mesh on a particular face using refinePDEMmesh().
FaceID = 1;
model = refinePDEMmesh(model,FaceID);