Originally Posted by kindraeventing
I would at least bring her back to a trot if not the walk, just keep the impulsion up and the speed down. Keep your eyes up, shoulders back, hands a bit wide to keep her straight, both legs on, and whip/spurs if you need/have them. Just be quite positive and convinced that she will go in, attitude is really important in that situation.
I agree with Kindra. This sounds like something you'll have to devote some real time to and school a lot of strange water to get her over it completely. Other than that you will just have to ride really strongly and positively and hope that she might trust you and hop in. Slower is better for sure, it seems like the exact opposite of what you want to do but it gives the horse more time to process what you are asking them and it's easier for them to see where to place their feet. Going faster gives them less time to see what's coming up and that's when they'll slam on the brakes at the last second and bad things happen. So I would choose either a strong trot or very short bouncy canter, making sure the horse is WAY up in front of your leg, and reinforce with your leg and crop if you need to.
Lots of positive schooling through water is the way to go though. Just lots of hacking on the buckle, through puddles, streams, whatever you have around, as long as the footing is good. With you being confident and supportive, and super calm and very nonchalant about everything, no getting excited, no fighting. Get another more experienced horse to lead her through everything at first if you are able. Keep at it, every day if you can, until she is totally relaxed about it, and it's not a big deal.
My mare gets super strong and excited on xc as well, just getting her RELAXED about everything has been by far our biggest hurdle over the years. It has taken a LOT of work, believe me! It sure has paid off though, now I can hack her around an xc course, she'll do all the (smaller) banks, up and down, and the water, including banks in an out, on a totally loose rein, she'll step up or down one foot at a time like she's out for a nice stroll, and she doesn't rush and is totally, 100%, relaxed about it. She's learned she can slow right down and take her time, it's not a big deal, but is always going forward regardless of what's in front of her. And that's the payoff for lots of positive schooling and time put in like I suggested above.
So when I go to a strange xc course, one of the first things I do is walk off a smaller bank into the water with the reins on the buckle. People look at me really strangely, but it's such a good exercise for us, reinforces the relaxation, the staying forward and straight, slowing down, looking where she puts her feet, and confirms her trust and confidence in me, even in a new place or water she's never seen. I think it shows a lot of confidence when a horse can do stuff like that super relaxed at a walk, without getting all amped up, and without much driving or interference from the rider, and that's what I strive to create in an eventer. A horse that is forward but relaxed and thinking about what's in front of them. Not all worked up and rushing and frantic to get over things. I show them where to go, and they just go.
So it's definitely something you'll be able to get over eventually, it will just take lots of time and work. Good luck