I don't doubt the accuracy of your Schemann quote. However the connection with what is being written about is still tenuous. Theosis is not mentioned in the section, so even if Mary is relevant to theosis the reader will not understand the relevance of Mary to the section. Moreover theosis is not about becoming God in the (ontological) sense understood by most Christians - therefore it is doubtful that theosis has any real relevance to the Nature of God - the section is about the nature of the God, not any Godlike state to which man might aspire. 
 ::::::If you really think that this stuff is relevant to the section then I think you have to add something in it about theosis and then the stuff about Mary can be used to back it up. For myself I think anything about theosis is not relevant. No orthodox Christian understands theosis as 'becoming of the same nature as God'.