You have to keep leg on all through the course, up to the base of every fence. A crop helps, to tap her if she starts ignoring your leg or hold on the side she runs out on if she does that. Keep a brisk trot or canter...you should feel like she's cantering "up" into your hands, is light on her feet, so she can spring over the jumps. She has to trust to you get her safely over the fences...riding assertively and telling her that she must go over will help her understand that you know what you're doing and will make sure she gets over safely. Understand when a refusal is your fault though (bad approach, wrong angle, not centered to the jump, etc) and don't punish her for it if it's your fault. I think based on watching your video maybe you aren't getting her straight to the fences so she is not in a comfortable position to jump. Make sure you keep your eyes up all the time, looking at your next fence, so you can direct her as best as you can. Use your legs, not your hands, to guide her. Remeber, your hands control her head and the bend of her neck, but your legs control the most vital parts--her body and legs! You cannot get away with a bad approach to a jump on a timid jumper...I know from experience. It teaches you a lot but can be frustrating! Just keep with it though...she will teach you a lot even though she will be harder and less comfortable to ride.
Also, some horses are hesitant to jump if the rider is pulling on them or hitting them on the back when they land...is your position good over jumps on this horse? It looked great on your video but maybe this horse's movement/saddle put you into a different position. All horses have different feeling jumps. Make sure to grab mane or slip the reins if you have to to avoid pulling her in the mouth if you get a bad jump...even professionals have to do it sometimes, and it pays off. Your horse will thank you and trust you more knowing that when you cannot hold a position, she can trust you to still give her the best jump possible.
Also make sure that when you are "encouraging" her you are not leaning forward and flapping your arms at her...this is a big fault I see with beginning jumpers. Keep your upper body and arms still and just use your legs, seat (and crop if need be) to keep her going. If you lean forward and get unbalanced she will just get confused, unbalanced and even frustrated because you cannot direct or balance her well and will refuse and hit poles even more. Especially with a timid jumper, you need to STAY BACK and quietly but firmly encourage them on.
Hope this helps! Let me know if anything didn't make sense...
He knows when you're happy; He knows when you're comfortable; He knows when you're confident; And he always knows when you have carrots.