There are any number of ways you could bring up the fact that you are married. You could bring it up it casually in coversation to get the topic started. You might mention your wife likes X-thing that this woman likes, etc. But I would be sure she is aware that you are married and also that you do not plan to see her again after "sealing the deal." If you plan to be at all ethical you should be sure she knows exactly what she is getting into so she can make an informed decision on whether or not she wants to get involved in this situation, however temporary.