ive ridden horse that get really really upset if they think theyre doing it wrong,and they panick and get flustered and then we have no hope of doing anything. im not sure if your mare is the same as mine, but in every little thing she does i say: good girl! and really comfort her. if shes new with jumping maybe try free jumping her??? i think it might help her find her balance and get more comfortable with going over the jumpes, without a rider on her back. once she is more confident in herself then maybe try a few grids, ive heard those are supposed to help with the horse and riders timing, control and strides. haha im a dressage rider, used to be hunter, so i dont really know that much, but those are just some exercises that i learned when i did jump :P hope this helped!!
Celebrity Jumping Exercises - Google Books i thought this was really good and mmight help you