River is definitely maturing and challenging me, but she's also becoming needy and velco-dogish. Her favorite thing is to sleep on the couch and have her head on my foot or legs while I watch TV. River was also kicked by a horse when she was younger and is understandably nervous about them.

I took her to the barn today and it was the first time I handled my mare, Quin, with my dog out of the truck. Quin could care less about dogs, but River was seriously freaked out. She kept trying to herd me away from the horse and kept jumping up at me almost as if she were trying to climb up into my arms. Her eyes weren't shifty or hard but I could see the energy exploding out of them.

Once Quin was grazing happily River and I played fetch with a stick, so she's not shut down or anything, she's just... over exposed I guess.

I'm going to keep taking her and exposing her to the horses, but what are some things I can do to help her relax? At this point I think an e-collar would be damaging, since she's obviously upset. My ultimate goal is to be able to bring her with me on trail rides in the spring/summer.

I can brag though. River was very polite to all the barn cats, made a bee-line for me every time I called her name, and she didn't try to eat horse poop.

In the barn my dogs have a safe cozy place aka the tack room.

I started slow. Harley was nervous around horses but use to get in high prey drive when the horses moved faster then a trot.

He now can be focus on some play or work near horses and he will be happy to be beside a horse that his mounted. Horses that are by themself still make him nervous a bit even when they are on leash. Cross ties is ok.

I am perfectly fine with my dogs not wanting to go near loose horses or be in my way when I handle horses.

I kept him on a leash or a drag line for a long time, but it is not very practical around horses, especialy young spirited ones.

The good side is that my dogs are fairly confident around horses and all my horses are good with stuff being dragged by a dog and flying ball.

The desentisation tread gave me a lot of idea but had to adjust to the fact that the horses are in direct sight from my living room.

Could it be that River was just wanting your attention? You with another animal isn't something she's seen before.
How does she act/react in the barn when the horses stick their heads over the stall doors? Curious,avoidance, aggression?

That's a typical reaction for a dog meeting a horse first time up close .
Having the dog sit or down on your jacket 10 or so feet away from the horse while you are grooming helps. The dog will get confidence as it sees that the horse doesn't plan to "get them", is in fact bored by them.

Most horses, like cats, affect total indifference to a dog, especially a pup. But they are watching.

Smelling a horses ankles and swirling around is dangerous.Being still and staying where the horse can see the dog is good.
Remember that your horse can strike as well as kick and may do that if the dog gets in front of her legs but below her head in a spot she cannot see.

When River is unsure or even afraid of a situation her reaction is to sit down kind of hunched with her elbows bent about 45 degrees. Whenever she was jumping up on me she was really trying to wrap her front legs around me and when I'd tell her to sit and calm down she'd hunch over on her elbows. I just don't think that was good attention seeking behavior. If anything it was 'please lets get out of here' attention seeking behavior.
She doesn't seem to have any reaction to the horses behind the fencing or horses in their stalls. It's up close and personal with nothing between the two of them that seems to get her.
She will run around the horse but she won't be close enough for a kick and I think she's probably about 10 feet away at the shortest. Plenty of space for Quin to keep an eye on her and not spook. When she runs around Quin she's not really doing it AT Quin, she's just running around that massive body so that she can get to the other side.

I would just take the time to get her used to the horses. Start far move closer over time.

Also mine had issue when I was with the horse or on at first. So it was to keep the dog bussy and at safe distance. Stuff kong, warm blanket help. Now I can ride and Harley will coach me from the mounting block and Dexter sleep in the horse blanket.

Harley used to follow at heel while I ride but some how that got boring very fast. Darn dressage horses going in circles all the time. In the outdoor ring the dog just play on the grass or hang out in the shade. Dexter was around since he was 8 weeks and Harley since he was 8 months.

Harley was a real challenge. It was over one year of work for me to trust him.

River was bolder today. I lunged Quin in the round pen with River on the outside until River came in through the bars and sat in the middle and watched us. She eventually got amped up and started barking so I put her away. After my ride I took her back out and we walked by all the horse pastures and played fetch.

The second day sounds much better. That doesn't sound like a fearful dog just stimulated by the horses.

Sounds like you're doing a good job. Just watch that he doesn't get over-stimulated.

It's interesting the different reactions dogs have to horses. Two of mine (a collie and GSD/Malamute mix)wanted to herd them. One Collie only saw horses a few times but totally ignored them.

My Keeshond, Misty, was the most interesting because she had a real affinity with horses and just seemed to know how to act around them. Her best friend and playmate (they definitely were playing) was a horse. And, one mare that would literally go after (seriously after) any dog that was stupid enough to enter her corral would allow Misty into the corral with her newborn foals.

Shelby (malinois/herding mutt of some kind) can't be at the barn. At all. She'd get herself killed trying to herd the horses.

Edited to add-

When River got kicked by the horse they were definitely playing. The horse didn't mean to hurt her, but it's a matter of physics! 1100 pound animal vs 25 pound animal.