It says "You will need to lay, slay and spellbind the essence of a very powerful hellhound to unlock the next seal". 

If I'm not mistaken, she's referring to the red skull on the 5th floor in Fire-Dominion. I've already killed and fuck her, but the marker still tells me to go to Fire-Dominion. And nothing happens when I sleep, even with a marker on the bed.

I have 4 active markers, 1st telling me to go to bed, 2nd telling me to open the Gallery next to the bed, 3rd telling me to go to Fire-Dominion, and 4th telling me to turn the spell page to the last session.

If someone can help I will get very thankfully!