Both Moiraine and Lanfear are alive, and Moiraine is not under Lanfears control. If you remember in TSR Rand, Mat, and Moiraine were all through the doorway AT THE SAME TIME, yet never met each other, and may have even asked their questions at the same time. This leads us to belive that there are several copies of FinnLand, and no two people are never in one at the same time. So, when Moiraine and Lanfear went through the doorway from Rheudian, they went into separate copies of FinnLand.(Its too bad Moiraine hadnt been through it already, 'cause then she would have just passed through, like Mat did in Tear,while Lanfear would have been trapped inside, but as well wish the DO did not exsist.To quote Perrin"If wishes were wings, sheep could fly").