Nervous Horse

I have a 17 year old mare who is afraid of the other horses. She goes totally right brain anytime she gets near another horse, and she kicks at them as they pass one another in the isle at the stable. This creates a problem for the other horse owners. She is a sweet horse except when she gets near other horses. I am at my wits end and need some suggestions. Her issue is fear. I do not know why she is so fearful but she is. You can sense it in her. She starts breathing faster and her mind goes totally off kilter. Any suggestions? This is the only time she does this. She does not spook on trail rides or passing vehicles, strange noises, etc. I just dont know what to do for her.