Willie I'm glad you're GF is ok. I think what she did -paying attention to your surroundings- is the first line of defense, and good for her to recognize a threat way in advance. I'm not real confident of pepper sprays because you must get it in the perps face for it to be effective. The time taken to get the spray out and pointed in the right direction could be better spent trying to get away from the threat.
I would also suggest having her file a police report. I know it seams pointless, but if you don't let them know there is a problem how are they suppose to fix it?