User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-31726296-20170801043036/@comment-4802891-20170803073250

I'm back with an answer.

If she is linked to the Fianna Knights as I suspect, she should be the daughter of King Underwaves, and her NP should the Beinn Eudainn Castle.