You click when she's performing the action, i.e. jumping (actually at the precise moment when she's already contracting her muscles and pushing off the side). Just make sure she's already at the point of no return, i.e. so that there's no possibility for you to click and her to stop the action (i.e. not to jump). If you're unsure or not good with the clicker, click when she's already in the air.
Do practice just jumping off random things, or over things (sand piles, tree trunks, stairs/steps, agility jumps etc.), not just off the one platform you have especially made for training the jump. You want the jump to become a reflex, where she'll jump even in just air when you say the word.
(Remember to train the jumps sitting next to her, or on the ground, not only when you're standing)
If you were to click when you say the word (instead of the action), you're clicking = rewarding for whatever she's doing at the time of the word. So if you say jump = click when she's sitting in the boat looking at you, you're associating the word with the stay (what she's doing at the time you click) instead of the wanted action.
So.. for training the jump..
Click when she's already jumping (not just wobbling about to go), as you want to "mark" the jump as the action.
I'm glad to hear that she enjoyed the trainings, she sure had good dogs so we were able to do quite a lot with the two
.