If you get cold sores frequently you can just take Abreva. I've had them my whole life, probably from a shared cup with my siblings or mother when I was little, and they never bother me. I've learned to sense how they feel when they first start to grow, and applying Abreva for the rest of that day nips them in the bud every time. Even without Abreva, they're not really bad. A little itchy and inflamed, but there's no pain or any health risks.
However, it's always good to be safe. If you like her enough and she likes you enough, the kiss can wait until hers flare down. If you have never had a cold sore, you are immune until you contract the virus. When you do contract it, you are then diseased for life. They spring up and go away at seemingly random intervals. Some people get them more frequently than others.