Rearing horse? please help:(?

So the barn brought in a new horse, shes about 7 years old. She came from and auction line and the only reason w bought her is because i knew her and worked with her befoe and she was great. Im used to working with rescues and neglected horses. This horse was bought by a young family, she was easy to catch, nice horse in general. now she is horrible to catch, and when you do catch her she freaks out and does a little dance on the spot, whens shes alone. shes good to tack up, bridle but you cannot touch her face. like her muzzle part , the vet was out and she dosent have any problems, and now shes been rearing. like out of no where, she will just be standing eating with the other horses and rear up very high. you can be walking her and shes fine and then she will just rear and try to run off, if you hold her by the reins she will freak out over nothing and rear and bolt away, when riding she fine, but whn you have enough contact, she will rear up. She reared in the barn a few times and once she hit her head on the roof. it was very scary, i though she really hurt her self , she kinda put her head down for about 30 seconds and her tounge was hanging out, so i shook a food bucket and she kinda gotout of it, i walked her and check her reflexes and she was fine. but now she wears a head bumper. how can i stop this? how do i correct her? do correct her with dicipline or reward? please help me, we can't afford another trainer, we have several horses under training that are worse then this. And we cannot sell her because no body will take her and im NOT sending er to the slaughter line up , where she was before.