She hasn't been announced, but
that doesn't mean she won't be playable. In fact, it's more likely that she's playable than not at this point, and she'll probably be revealed in the near future.
It could be:
August 7 = Margaret
August 14 = Mitsuru
August 21 = Game's opening or a bunch of new content like modes and stuff
August 27/28 = Game's opening
I'm surprised there are still two "???" tabs on the website, and that they haven't added the "Network Mode" yet despite it being shown off two weeks ago via Famitsu and PV3.