Except if it was so terrifying, why did she do everything but call the police, who have the powers to actually investigate things like this and would have probably figured out in about 5 minutes who sent the emails?
I had it happen to me once, for real threats though (at least they were really being made, not that they came to pass). He said when he was going to come over, which should have made it obvious to me that he didn't intend to follow through, but I was young and stupid. I didn't call the police. I just invited a couple friends over. I figured if he wanted to come get his ass beat it would be an entertaining evening all 'round, except for him.
Now, my reason is obviously not hers (and I'm a vastly different person now), but claiming to understand how a person who feels threatened will respond shows more hubris than awareness. Maybe she was embarrassed to tell the police she was scared, maybe she got laughed at by an authority figure when she was young. Or maybe she didn't want to waste their time with something so inconsequential, maybe she had an authority figure scold her for wasting their time.
Or maybe she's a dissocial opportunistic asshat. But you don't know that based exclusively on the fact that she did not call the police. Why don't abused women call the police?