Even Ha'Ezer 62:7 says that in order to say Sheva Brachos at the meals that are made for the week after the wedding for the Chassan and Kallah there needs to be a Panim Chadashos (new face) present. Can a lady count as a Panim Chadashos or only a man?
Rabbi Mordechai Farkash (from Bellevue, Washington) suggests that this is dependant on the reason for the requirement of having a Panim Chadashos to be able to say Sheva Brochos. The Rambam (Hilchos Brochos 2:10) implies that when there is a new person present who has not yet heard the Sheva Brochos he becomes obligated to say them, which is why we can recite them again. However the Rosh (Kesuvos Siman 13) rules that even one who has already heard the brochas can be considered a Ponim Chadoshos if he did not participate in the eating at that time because his presence causes an increased level of joy. It would seem that the Rambam would require a male to be the Panim Chadoshos, because it must be someone who becomes obligated to recite the brochos himself. The Rosh on the other hand, would allow any one who brings additional joy - including a women - to bring the joy and thereby create a new obligation to say the brochos.
The Shulchan Aruch (EH 62:8) rules in accordance with the Rosh (that the requirement is because of joy), and it would therefore seem to follow that even a women could be counted. However, the Pischei Teshuva (:14) cites the Zechor Le'avraham that a women can not be considered the Ponim Chadashos. Rabbi Farkash concludes that common practise is not to use a women, and proposes that this may be due to issues of modesty.