she does know the one rein stop, but it hasnt helped, I did try it for a while, then I tried stopping her and giving her a sweetie, that didnt work either. When im on the ground walking beside her she's good, and stops when I stop, but yeah Bubba13, i've found that I have to pull her in the mouth to get her to stop. i've only had her since may, and when she first came she stopped ok, I think she doesnt now because im asking a lot more of her, so yeah i'll try that and saying woah at the same time, thanks
If she stopped before, but doesn't now, then something changed. Several things can make a horse uncomfortable with stopping. Does her saddle fit properly? What kind of bit are you using? Is it the right size and adjusted correctly? In terms of bits and bridlework, I recommend a simple cavesson setup with a plain snaffle of whatever configuration (single joint, double joint, loose ring, full cheek, eggbutt... ) your horse prefers. A double jointed loose ring is pretty popular.
Next, horses don't stop doing simple, foundational movements because riders start asking more. Honestly, if your horse cannot halt, then your half-halts described above aren't true half-halts. Odds are that, if there is not a physical reason for your horse to refuse to halt, then either she never learned correctly or your aids are not allowing her to do so. I went through this with my own horse, who I bought as a greenie. He simply never learned, and at the time I knew little better than to pull on his mouth. I ended up in the same place you're describing - an ok "downshift," but that final transition from walk to halt was a battle.
Really deconstruct and analyze your halt aids. It takes the entire body, not just your hands. Ideally, you want to do this with a "handshake contact" on the reins, but you may need to start on a slack rein if she's very resistant to the bit. Really sit down, you want to feel like you're melting into the tack when you're ready to halt. You want to keep your legs in that "on but neutral" position in order to maintain forward energy - every movement is forward, including halts and rein-backs. Squeezing sends mixed signals, but you don't want to take your leg away. The final piece of the puzzle is the hands, but the key there is that they are simply closing, not pulling. Think about stopping the following motion of the head - that closes the door. Seat into legs into hands. Ride her into the bit, bring her up to the bit like riding her up to a wall. Don't try to bring the bit to her.
This combination of aids essentially allows the horse to come down into a lower gait or a halt. Using different aids hinders the horse, makes it harder for her to downshift. If your seat is still moving in-gait, then it is creating energy that resists the halt-motion. Squeezing legs reinforce the gait, disallowing the halt. Removing the legs loses contact (contact is about more than hands). Pulling back creates resistance and inverts the spine, making it biomechanically difficult for the horse to halt nicely.
Very often, our horses' little problems mirror our own. I personally found that when I started being a real stickler about my own position and application of the aids, a lot of the really frustrating little problems I was running into with Scout just went away. Good luck, and happy riding!!