I hope all goes well for your friend. IMO, I think the best course of action for your friend to take is a "zero-sum economics" approach: the less the guy comes into contact with her, the less fuel his interest is fed. Hopefully, the system can be shut down by not receiving any input.
For day-to-day practices, I recommend she do what she can to avoid crossing paths with the guy. As yam said, she should change her phone number (a necessary pain-in-the-butt), park her car in the garage, alter her arrival and departure times from work (she could explain the situation to her boss/trusted co-workers and enlist their aid), always walk with someone to and from her vehicle, and change her normal hang-outs, for a bit. In short, lay low and make herself scarce. She should also leave the suggested paper trail, in the forms of police calls and a personal log of contacts. And, as a necessary precaution, she would be very prudent to get some form of physical self-protection. It should be something that is easy, quick, and reliable to use, as well as effective. Ideally, this aid will never be needed, but it should still be acquired and practiced with. Finally, if she doesn't have a dog (or two), she should seriously consider getting one. These are the basic actions I believe she should take to protect herself.
With this guy, I think that 2 results are most likely: he will either lose interest and move onto a new target/obsession, or he will go from annoyingly persistent to full-out stalker. The hope, of course, is that if she drops off his radar, he will respond in kind. However, time will tell and she should prepare for different possibilities.