That route along the Springwater corridor is creepier than it needs to be early in the morning in the dark. Your fear is totally understandable.
I would say, however, that riding across the Sellwood Bridge in the dark is fraught with considerable more peril. "Accidents" due to driver negligence or bad luck (new pothole, wet and slick bridge joints, crazy pedestrian who walks right into you) would be much more calamitous there.
You could try a few options for the Springwater section between Sellwood and the Hawthorne:
1: Fight back: zip ties and a mace holster under your top tube.
2: Safety in numbers: loiter slowly around the beginning of the trail there by Oaks Bottom until you see another rider roll through, and sit on their wheel (ride with them). Most people will appreciate the extra light.
3: Disguise: fake mustache
My wife has similar issues riding by herself. She doesn't like it. Worries she'll get a flat or other mechanical. Feels anxious and unsafe. Worries she'll get harassed or, God forbid, worse. So it sounds not uncommon. Maybe other women could chime in about it? Especially those who ride often and have dealt with it?
Hey PoPo: anything you can add from the police perspective? Do they give you guys training in defensive riding or ways to avoid, I dunno, being dragged off your bike?
Lots of luck. Me saying the following doesn't make it so either in your mind or reality, but you'll likely be quite safe riding that stretch. That said, I'll do a quick check of crime stats and see if I'm full of it. (Crime mapper stats here