She failed in CWC, and so tried to manipulate Cristal-like Law instead to achieve the same goal.

I see this stated a lot and I think it is a misconception that the CWC could be used to achieve the same effects as the Crystal Tower/Transparent Law. That is, unless Nocturnal knew more about how to use the Clockwork City than Sotha Sil which I doubt considering she did not construct it.

The Clockwork City is not omnipresent, nor seemingly effective beyond Mundus by its very nature, thus provided no utility to Nocturnal's endgame. Controlling CWC was part of the Triad's (obscure) goals though. But CLL was Nocturnal's primary focus all along and something she had spent hundreds of years, whatever that means in Oblivion, preparing.

Your assumption is correct. Nocturnal's true purpose in invading my realm was to steal my secret for utilizing life energy as a power source. I suspect she plans to use my technique to amplify the Crystal Tower.

It took Nocturnal hundreds of years to put all the pieces of her plan into place. And you wiped it all out with a single thrust of the Dawnbreaker. There will be other plans, I'm sure, but this particular threat is over.

Using the CWC or any other medium allowing her to exert influence directly on Mundus or control it would have made her plans easier but it likely wasn't going to be used to achieve the same thing.