Yes, it seems that all Mary has encountered is shallowness and trickery. But it is also possible that she can not look deeper because she herself lacks the feeling and wisdom that comes from feeling herself and reading. It is not surprising that she can not read Fanny's feelings, but she can not quite read Edmund either. Mary can only see in Edmund what she wants to see. It is possible that she has never met anyone like Edmund, but I think that she wouldn't have known the difference between affectation and genuine feeling.