This also establishes that the Blackbird River is in the Duchy of Blackbirdriver, but only barely, in the northwest corner.
Ibronka appears to live in the lowlands south of Blackbird Mountain, in Larkspur Manor:
Since the Manor was built with stones brought up the Elbow River, I think the Manor is on the Elbow River. To determine where exactly while require some speculation.
Let's step back a minute, and consider this road: it starts somewhere in or near the Kanefthali Mountains and passes through Hartre, with Lorimel in between.
Looking at Steve's Map, Candletown seems like an obvious stop off along the road, both because it's a port and because the road has to go around the ocean at this point anyway. There's also a reference to stables just east of Candletown:
It appears the Grand Canal connects to Candletown from the east, so I think Bevinger's House is actually closer to east by southeast than east. As to how far, "just east" is pretty vague, but I think that's probably less than a day, so I guessed about 25 miles.
I drew the Great Northwestern Road going from Candletown south by southeast to Bevinger's House, then straight from there to Hartre. At the point this road crosses the Elbow River, I put Lorimel, and then I put Larkspur Manor 9 to 12 miles (my estimate for 3 to 4 hours of traveling) back north along the Elbow River.
This unrealistic straight line version of the Road would appear to run right very close to Cargo Point (a location on Steve's Map that doesn't appear in any of the text as of release 3).