Adventures in horse sitting

My trainer is out of town, so I have been caring for her horses. She has 3. A warmblood gelding that I lease, her paint gelding, who is the alpha of the herd, and a 3 year old filly she's only had for about a year now. The warmblood that I lease is very mild tempered, and gets pushed around by the other two. The paint is just being dominant, but the filly is just mean. She is the smallest and is terrified of the alpha, but has no problem pushing around the warmblood. She bites and kicks and charges him, even if he is no where near her. I show him, and he is always cut up and has terrible scarring from her. She is mean to people as well. If anybody walks by her she put her ears back and shows her teeth. I have been doing a little Parelli work with her, but I really just don't know what to do. She is mean for no reason that I can see, and I'm really tired of her being so rude and hurting the horse that I lease . It has gotten worse sense my trainer left, so I will talk to her when she gets back, but until then, any suggestion?

She could just be bad spirited. Or she may have been abused in the past, or she is season, a number of reasons. Does she try to attack you? Also, try moving your leased horse to a different paddock where he can see other horses (if he has to be alone in the paddock) but she can't bully him