Re-reading the Lord of the Rings, Chapter 49

As before, the battle goes this way and that, but for once lack of discipline doesn't equate undoing, for fate itself is on Gondor's side.

The Witchking of Angmar symbolises the psychological element of war and it's thus only fitting that he'd be slain by a woman, for the psychological element targets civilians first and foremost.

Like in all battles Tolkien takes great care to let things come about in a believable way, the movements of the armies are almost choreographed, the Dead don't fight on the fields of Pelennor, but Aragorn brings many men from the south, so the summoning of the Dead can be interpreted as a symbolic version of the rallying of the coastal people.