Freyja is the Admiral and the superior to the captain/master.

She is a mature woman that is very frank to the captain because of his inadequacy.

To her, the captain/master is a very nonproductive lazy person that needs to be reprimanded.

To voice act her, image pretty much a strict principal that is sometimes slightly your friend, but most of the time you're scared of and the principal knows that you're scared.

Act as the principal.

I imagine her to have a mid-low ranged voice 

She has not va so do your own impression!  And make sure it's commanding!