The reason Nefreti said she couldn't help Keltham in any way is that if Nethys just said to Asmodeus 'look, that there mortal is going to destroy you unless you accept our compromise', Asmodeus would check if Nethys put that mortal there to pull that off. It's important, that Keltham is not a cleric of Abadar, not assisted by Nefreti Clepati, that humans, alone put him where he is, because it wanted Asmodeus dead -

The reason Nefreti said she couldn't help Keltham in any way is that if Nethys just said to Asmodeus 'look, that there mortal is going to destroy you unless you accept our compromise', Asmodeus would check if Nethys put that mortal there to pull that off. It's important, that Keltham is not a cleric of Abadar, not assisted by Nefreti Clepati, that humans, alone put him where he is, because humanity wanted Asmodeus dead -