I need help with a angry old horse?

It seems like she's had a bad experience with other animals in the past. She's an old horse and so completely re-teaching manners is near impossible. You can however try and get her to be slightly 'calmer' around animals. You say she has no problem with people, so approach her with an animal in your hand. She might be a little confused but she'll slowly start to understand that animals can be just like people - nothing scary - and nothing threatening! As for your other horse, have them both on a halter and try leading them towards and away from eachother untill eventually they don't take any notice of eachother. Remember this'll take time and patience. Your other horse is now afraid of any other horse it sees. Is there any chance of you putting her in a paddock with another non-agressive horse? He/She'll get used to the idea that not every horse if aggressive and out to get her. I really hope this helps.