Like Brianna said, allow your horse to look at the jump first. Try to go from your normal approach then. If that doesn't work I'd suggest trying to identify what about the jump your horse is refusing. It might be decoration, the height/angle, or even something beyond the jump. Looking for differences between This jump and the ones you normally jump might help as well. Good luck!
Approach the jump first to let the horse acknowledge it because sometimes horses refuse out of being surprised then go straight to it from a normal approach so the horse has plenty of time to be prepared. If the horse still refuses come at the jump from a shorter approach so they don't have much time to think about it and right before the base use a crop frimly behind the leg. If the horse jumps approach again and use the crop with less force just let the horse know you are with him. While doing all of this make sure you are pushing your horse off the leg and into the bit (holding contact with the reins) to create impulsion which makes your horse confident and balanced ( impulsion should be used all the time when riding)
Hey Hannah I say use your leg and a whip maybe try lower jumps that it can walk over if it refuses and then go higher
Is it a different jump? Is she stopping dead in her tracks or running around it? If she's running g around it it might be a steering issue more than anything so maybe use two poles either rodeo for the jump as wings to encourage your horse into the jump. Maybe try lowering the jump, make it easier and then work you way back up? Also maybe sure you're not pulling on her mouth because that would encourage her to stop. Also make sure your horse has plenty of time before the jump to see it (at least 4 straight strides). Maybe carry a crop and make sure she is in front of your leg and has an active canter and if Sheba stops first time make her halt and stand in front of the jump so she can see it. Then come around again, and if she's stops make her stand in front of the jump and give her a kick or smack with the crop, then come around agin and she should jump it.