Levia must have used these runes to aid her ritual. Even if she is as powerful as Modera says, she was a novice in demonic magic, so the runes must have helped stabilize the portal.
I'll need you to find out what runes need to be activated to recreate her ritual. There are several books on runic magic in this room, which she no doubt studied for her ritual.
Once you have activated the runes, I will complete the spell.