Where can i find more info on her realm and stuff in her realm? UESP just doesnt have enough.

Battlespire had a portion in which you were in her realm I think. Otherwise, I would say it would reflect her, extremely pitch black. Expect to bump into walls or fall in chasms

http://www.imperial-library.info/content/shade-perilous gives us a little on Shade Perilous.

http://www.imperial-library.info/search/node/nocturnal

That's pretty much every instance that Nocturnal is mentioned in the series. Maybe a few extra things as well.

There's a line or two in Infernal City about Nocturnal's realm although I'm only guessing. It's not called that by name.