Jadis, the White Witch, is my favorite villain in CoN.
But Jadis is not the Green Lady in The Silver Chair. I will quote a couple of passages from the book that should end all doubts:
(In response to hearing that Prince Rilian is still alive, Glimfeather says): "'That almost makes it worse....It means she has some use for him, and some deep scheme against Narnia. Long, long ago, at the very beginning, a White Witch came out of the north and bound our land in snow and ice for a hundred years. And we think this may be one of the same crew.'"
And: "...now they all saw what it meant; how a wicked Witch (doubtless the same kind as that White Witch who had brought the Great Winter on Narnia long ago) had contrived the whole thing, first killing Rilian's mother and enchanting Rilian himself."
The Green Lady is much like to the White Witch, in that she practices sorcery and the like, but Lewis does not tell the reader that she is Jadis. Rather, he writes that she is of the same kind and of the same crew. The Green Lady is a baddy, but nothing like Jadis (and note she wore green and was known as Green, whereas Jadis was later in Narnia called White).