"You'll never convince me, Imaen," said the Venerable Orn. "Might as well try talking the River Wenn into a new course." Hunched beside me in the bench seat of the cart, Orn wore a smug grin. "Abandon the temple, lass, and you'll always regret it."
"I've made up my mind," I said. "Why can't you understand?"
"But you've a tender heart, and you've seen how the dying trust you in their time of passing."
"That was before Cambryn Island," I retorted, hoping to put an end to the argument. Gazing out across the silent waters of Blackfen Bog, I watched a crane spear a black fen ray with its beak. A shiver stole through my robes. I could blame the chill on the early spring air, but I would be lying to myself. The

"You'll never convince me, Imaen," said the Venerable Orn.
I had a hard time getting my bearings about who was talking to who here. Maybe you could just change this dialogue tag to say "the Venerable Orn told me." that way I know immediately that Imaen is the POV 1st person.

"Might as well try talking the River Wenn into a new course." Hunched beside me in the bench seat of the cart, Orn wore a smug grin. "Abandon the temple, lass, and you'll always regret it."
"I've made up my mind," I said. "Why can't you understand?"
"But you've a tender heart, and you've seen how the dying trust you in their time of passing."
His response here doesn't really follow the question Imaen asked (why). You could just change the "But" to a "Because" and I think I would have got it easier.

"That was before Cambryn Island," I retorted I would prefer a simple "said" here, YMMV, hoping to put an end to the argument.

Gazing out across the silent waters of Blackfen Bog, I watched a crane spear a black fen ray with its beak.
This sentence as constructed was hard for me to get through. You could try something like this:

I gazed out across the silent waters of Blackfen Bog and saw a crane spear something small and dark, then disappear.

I know that's not great, but it eliminates the things I stumbled on and had trouble thinking were possible. I'm sure you can do better.

A shiver stole through my robes. I could blame the chill on the early spring air, but I would be lying to myself.nice The sun sat low on the snowy summits of the Moonfall Mountains[; dusk would soon be upon us,] -Cut and after traveling the bog for three days, I knew what happened at dusk.

From the word "Gazing" onward I thought it flowed beautifully, and now I want to know "what happens at dusk." I'd love to read the rest, but I can't promise how quickly I could get it back to you.

I do agree with Alliedfive about the confusion of who is talking in the first paragraph.

When you are ready, send it on. I'd like to read.