I read this theory about Denna being Haliax and this theory came to my mind: 

We know Lanre's wife, Lyra died. But How? 

Maybe giving birth to a child!? 

A girl with het mother's beauty and voice !?

A girl with Black hair named DENNA ?!!

And She hates her father for the terrible things that he has done? So she wants to stop him by joining the order of  Amyr with help of "Master Ash" ?

Or She is helping her father by going inside of Amyrs and help to destroy them from inside? 

P.S: in this theory MASTER ASH is a member of the order of Amyr 

Thanks for reading, I'd like to know what's  Your idea about this theory