Moondance,
Perhaps, being in the 12th house, it indicates karma from a past life. Perhaps she DID harm you in a past life. Finding it in the chart may have dredged up the fear of her in your emotional memory. The karmic responsibility then, would be to forgive her, and get rid of any suspicion that is unfounded. Sometimes the worst of enemies in past lives can be the best of friends in this one. The karma would be to work towards true loving friendship, instead of shutting her out and expecting her to be that way towards you again. That's the purpose of it coming around again - to get it right this time.
On the flip side, always be alert for true warnings from the Spirit that you are in danger. However, the false suspicion will usually cloud your inner warning system. The key may be this: Were you suspicious and fearful of her before you found out about the Arabic Part of Secret Enemies in the 12th house conjunct her sun?
All the best,
Freedomlover