Oh, wow. Your first paragraph is absolutely beautiful. Lush and detailed with the description, but the RIGHT description to help me “hear” the MC. What does she experience? The wind whipping her hair in her face. We move from her immediate experience to the outer one. Just great.

Yup. And your whole entry does it. I even love the conversation. Again, something mundane that tells us more about the bigger picture of their relationship. If I’m nitpicking, I’ll say to make sure the dialogue sounds true – read it aloud, and I bet you’ll want to change “Just as she always does” to “like always.”

(So, there’s a tip. Read your dialogue out loud to make sure it doesn’t sound weird or forced or unnatural in any way.)

But, yeah. This is beautiful. So nicely done. YAY VOICE!

Oh my, I LOVE this. I love the lush and crisp voice, I love the easy banter between the siblings. I love that you give us enough information to understand what's happening. It's a great start!

The voice also feels historically accurate to me, although I do agree you can make the dialogue a little bit more natural. But really, this is a fantastic start! Very well done!

One nitpick: since you're leading the first sentence with "horse's hooves", you can't actually use its in the second independent clause. It would refer to either the hooves or the hillside, not, actually, the horse.

Bransfield Estate, Gloucester, England 1825

The horse's hooves thunder across the hillside, and my heart pounds with each bunching of his muscles. My hair breaks free of its pins, pale strands sweeping across my cheek. Though the cold wind breaks through the thin barrier of breeches and tall boots borrowed from my brother’s wardrobe, the wide smile never leaves my face. Mild discomfort is a small price to pay for a ride in the country unhindered by the thick skirts of my riding habit.

I glance at Robert, who is keeping easy pace with me.

"Careful, dear sister," Robert calls out, the wind snatching at his words, "I'm gaining on you."

I laugh. "Serenity will refuse to jump this next bank, like always."

I press my booted heels to Orion’s sides, and a little thrill jolts through me as he charges forward. Excitement bubbles over my skin, making it hard to distinguish from my own. The magic which connects us fills my mind with a flood of images; the way the light layer of snow gives way beneath his hooves, how crisp the air smells when he takes deep breaths, the light pressure of my weight on his back. The mare behind him is on his mind too, a speck of awareness I take advantage of—it tells me how close I am to reaching the creek before my brother, therefore winning our little race.

The bank jump approaches. It’s nothing but a fallen log on a hilltop, but from this direction, the horses will have to jump down nearly four feet.

Your writing here is very descriptive and lyrical, which I think fits your genre perfectly, and the setup gives a very clear sense of your MC and her personality. There are just a few places here and there where I think you say in 10 words what you could say in 5. Cleaning up those areas will help keep the pace quick and smooth.

IN-LINE CRITS

Bransfield Estate, Gloucester, England 1825 (If there's a way of working this information in early on without subtitling it, I'd suggest doing that. Not a huge thing, and more of a personal preference of mine, really.)

The horse's hooves thunder across the hillside, and my heart pounds with each bunching of his muscles. My hair breaks free of its pins, pale strands sweeping across my cheek. Though the cold wind breaks through the thin barrier of the (added definite article) breeches and tall boots borrowed from my brother’s wardrobe, the wide smile never leaves my face. Mild discomfort is a small price to pay for a ride in the country unhindered by the thick skirts of my riding habit. (This is one of those sentences that I think could be a bit tighter. For example: "Mild discomfort is a small price to pay to ride unhindered by thick skirts." We're already aware that they're in the country and the riding habit isn't a detail that's altogether necessary.)

I glance at Robert, who is keeping easy pace with me.

"Careful, dear sister," Robert calls out, the wind snatching at his words (I like this phrasing.), "I'm gaining on you."

I laugh. "Serenity will refuse to jump this next bank, like always."

I press my booted heels to Orion’s sides, and a little thrill jolts through me as he charges forward. Excitement bubbles over my skin, making it hard to distinguish from my own. (I had a little bit of a clarification issue here. It may be just me, but I wasn't certain at first who she had a connection with. I thought it was her brother at first.) The magic which connects us fills my mind with a flood of images: (changed semicolon to colon) the way the light layer of snow gives way beneath his hooves, how crisp the air smells when he takes deep breaths, the light pressure of my weight on his back. The mare behind him is on his mind, (added comma) too, a speck of awareness I take advantage of—it tells me how close I am to reaching the creek before my brother, therefore winning our little race. (I don't think you need anything after "brother." To me, if she wants to get there before her brother, then I already guess that they're racing.)

The bank jump approaches. It’s nothing but a fallen log on a hilltop, but from this direction, the horses will have to jump down nearly four feet.

Beautifully written, and the revision to the dialogue works. I'm connected to her voice and I'm curious about what's going to happen on this ride. I don't have any further suggestions than the ones Becks has given. Loved it!