Rearing is an extremely dangerous behavior. Before you assume it's a training issue, you need to look at the whole picture. Is she being kept the same as she was at the old barn. Was she stalled or pasture kept there, and how are you keeping her now? Have you changes her feed regimen any, if so, how? Does the saddle that you are using fit her properly? Have her teeth checked if that has not been done lately. If all of this checks out, then it's safe to say that it's a training issue. And it's a major issue that not everyone is equipped to handle on their own. It's a hard habit to break once they start doing it. You definitely need to get the assistance of a trainer in solving this problem, or just send her to a trainer, which would probably be your safest bet on this.
I know how frustrating it can be to have a horse that has a habit that intimidates you! I had one with the same habit when I was 14, but his was worse, he would actually throw himself over on purpose. This is what he was known for, not being a good barrel or pole horse, but for rearing up and flipping over! My mother actually had people ask her what the hell was she thinking buying a horse like that for a 14 year old! I rode him for over a year being scared of him, because every time I picked up the reins, my uncle would yell at me to get out of his mouth he'll rear up! But I knew exactly what caused him to rear, so I knew how to fix it. So between two show seasons I fixed his problem. I taught him to yield to bit pressure and to drop his head when he felt pressure on the bit. By the beginning of the next show season, he would work collected like a WP horse. My uncle actually told me that I ruined my barrel and pole horse by doing that! That is until I ran, and it cut off about 2 seconds from each pattern. He went from being a 18 second big pattern horse to a 16 second big pattern horse on barrels, and from being a 23 second pole horse to being a consistent 21 second pole horse with some 20 second patterns thrown in there! I owned him for 5 or 6 years, and never had him rear up on me, and after that winter I was never scared of him again.
If you can figure out why she is rearing it will make the process of fixing it a lot easier, but I still suggest getting a trainer! Good luck and God bless.