Horse dominance issues

[Ginevive]

Wow, this post came out pretty long..!
This is not an issue with us and the horses; it is between the two of them. We got Emma (the white tovero) last November, and Cuesta came along in the end of December. Well, right off the bat, Cuesta was the dominant mare; she put Emma in her place, and was the one who determined where they grazed, when they drank at the water trough, etc.
Then last spring, they both foaled and the foals were here until September. Nothing really changed then; though Emma foaled first and was extremely protective of her little man, and didn't take %$#@ from Cuesta.
Well, seems now like Emma is taking over. A few nights ago we got home around midnight, and let them in as usual at night; Cuesta had a swollen, black eye. We were nervous and about to call the vet the day after (Monday) but her eye looked perfect the next morning.. point is, Emma has been beating on her (nothing that serious, a few cuts and bite marks.) I know that this is normal in a herd (even this small herd of two) But I just wish that they would settle into a "routine" again and have a leader determined. I let them in at night.. they have to be led down a small lane w/ fencing on either side, and I would always lead Cuesta and Emma would follow.. Now there has to be a scuffle before they get to me at the gate. I will NOT open it until they have settled, but now Emma is usually first there.. argh!! Any horsey behavior experts have any input? It is not a problem per se, just odd.. seems like once people started coming out and hunting back in the woods more in the past weeks, this has been going on.. Cuesta is VERY interested in the hunters in the woods, though she can't see them.. STARES out there for minutes on end.. maybe Emma saw this as a weakness in her leader, an opportunity?
Here's their "setup": Barn, two 11x11 box stalls adjoining each other. Roughly 5 acre pasture, across an access road; I string up some cords of rope across this road to lead them in/out; tube gate.
Here are some shots from yesterday morning..
The gate area:


Emma


Cuesta