SOLVED. Looking for fantasy YA book, priestesses, magical border, possible trilogy [s]

[Emily]

The main protagonist is female. I remember a group of women, as priestesses. It was like a coven. Protagonist is an initiate of some sort.
There was also a border they had to maintain and repair with magic. They would do regular patrols.

A monster of some sort comes through the wall, and they have to fight him off. I also listened to an audiobook of it and remember them singing spells of some sort at this point.

A man comes through border, and the female protagonist heals him. He makes walking sticks, I think. They leave the group together for some reason. I remember a city with docks and ships.

I feel like the author's last name was either Bishop or Priest. It was part of a series, maybe a trilogy.
It was young adult fiction, but I never read more than one book. The book I remember was an orangey color. I think it was around 2005 or 2006.

I don't have much to go off of, but I hope someone knows!

[Bec]

The Singer of All Songs from the Chanters of Tremaris trilogy?

[Emily]

YES. THANK YOU.