I don't recall the context, but my colleague responded to a question by saying, "Something that terrified me - still terrifies me - is closing up the park late at night." Honestly, and I'm not trying to be macho here, being alone in the Park at night doesn't bother me. Then again, I am bigger and taller and much, much more experienced than the other Ranger.
That's not the point.
The point is she is afraid doing what she does for a living - at least part of the time - and that really makes for a miserable life. I wouldnt wish fear on anybody, especially when one has to do it day after day, week after week.
My suggestion for her, and for all other civilian Rangers, is to attend at least one self defense course, particularly one taught by a former police officer. Ask him or her for pointers on what is most frightening to you. Then, when out alone, analyze every situation that has been frightening, or could likely occurr. Think of potential escape routes for every location. Forget the 'face to face' aspects of making your guests feel welcome. Do that in the daytime; at night, or in remote places, do it from the vehicle with your foot on the brake. If something goes amiss, floor it. If you get spooked by something, get away from it. Plan your work so you are in more developed parts of the park late at night.
And lastly, recruit help. They don't even have to know what you are doing, but you can increase your safety by stopping by a campsite occupied by a friendly camper on your way to the lower forty to have a chat. As you leave, casually mention where you are headed, and throw in, "It shouldn't take me more than ten minutes; I have to be back in this area as soon as I can." If much more than that elapses, hopefully he will take a look or call somebody to check on you.
I can't say it too often: Plan it in advance.