I think horses believe that the little fishys and frogs will eat them :)
First I have to ask if you were in a group, did the other horses jump over it? She may have just been doing follow the leader. If not, you need to work on her water fear. If Steve's horse doesn't jump, let him go first with your horses nose right in his horses butt. If that doesn't work, go to the crossing and get her as close as you can without crossing then turn away, keep getting her close and turning away. (advance and retreat) if she puts a foot in give her a good girl and retreat. Just let her do it one foot at a time. Let her put her nose down and investigate it. If she acts like she is going to jump turn her away from it. It will take some time but she will get it, have patience and have fun with your new horse.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France