Why was this?
I take it that she had made arrangements for leaving the tomb when, after her resurrection, she should be a new woman, with a different personality, and less inured to the hardships that in her first existence she had suffered.

So far as we can judge of her intent, all things needful for her exit into the world had been thought of, even to the iron chain, described by Van Huyn, close to the door in the rock, by which she might be able to lower herself to the ground.

That she expected a long period to elapse was shown in the choice of material.

An ordinary rope would be rendered weaker or unsafe in process of time, but she imagined, and rightly, that the iron would endure.
"What her intentions were when once she trod the open earth afresh we do not know, and we never shall, unless her own dead lips can soften and speak.".