There is nothing to be afraid of in working with an enemy. According Robert Green, working with an enemy is better than working with a friend, because working with an enemy would make you set your objectives aright without any form of sentiment. But with a friend, you would notice that there would be so many emotional issues that would be taking toll on the overall output of the business.
But in a case whereby your enemy is trying to thwart your efforts, especially if he/she is your superior, you would have to seek the intervention of a higher authority. But if the enemy is on the same level with you as coworker, you have to keep her at arm length.