I myself had been at the meeting to decide to build this fortress and watch tower, feeling it would at least give us a warning if Jadis decided to attack us again, but had not been directly involved in its building. Mostly the Red Dwarfs and Centaurs, along with help from others, constructed it.
I am sure Jadis’s spies had informed her of the construction of the Watch Tower, but I think the only reason she didn’t attack it at that time was due to Piter returning, expressing an interest in finding his brother, and asking Jadis for help.
I doubt Jadis really cared if Khol was alive or not, or what had happened to The Rising Moon, but she still desired a way to destroy the Tree of Protection, and the hag had said the scales of the Dragon of Darkness where a way to do that. Her problem was that the Dragon of Darkness was supposed to be on some island in the sea far to the north. She also knew that Piter had a ship of his own, the Endermen. That made her smile.
After agreeing to help Piter, Jadis went to see the hag who had been imprisoned in her dungeon for the last year. This time she asked the old woman to tell her exactly where the Lonely Island was.
“In the Gray Ice Sea,” the old hag replied.
Jadis gritted her teeth in frustration for a moment before asking, “where exactly?” Answer me truthfully.”
The old hag turned her head to look at her, although her eyes were closed as if sealed shut. With a sigh she spoke, saying, “on the border between eternal night and eternal day. Twice, when the hands of the clock are at twelve, look to the lone star in the sky. It will point the way to the Lonely Island. A great, gray land of rock and sand it will be, appearing like melted candle wax surrounded by a frozen dark gray sea. The dragon you seek sleeps in the pit of the volcano at the center of it. But be warned, she will not give you her scales as a gift. You must be clever.”
This information Jadis gave to Piter, although she lied a little and told him that the old hag had said that was where his brother was, but she could not say if he was alive or not. Piter was eager to leave, which was what the witch wanted, so she gave him whatever help he needed to get his ship, The Endermen, ready for the quest. She also sent Iron Boot with him, probably for no other reason than to be rid of the Black Bearded Dwarf, whom she had grown more annoyed with over the last year, and had been considering turning to stone and tossing over the high tower railing herself. While that would be moderately satisfying and somewhat entertaining, having the Dwarf go with Piter as an observer and report back to her on all he had seen, would be more useful in the long run.
Shortly after The Endermen departed on her voyage, Jadis attacked our watch tower for the first time, destroying much of the outer wall and fortress. The only reason, I believe, that she was not able to totally destroy it was because of the power of the Tree of Protection, which repelled her and her army.
Two more times she did attempt to destroy the tower, and both of those times, her attacks were repelled.
No doubt that enraged her further.