I'd first have her checked by a vet to make sure she's physically OK and is not in pain due to a health issue. Dogs don't show pain as humans do and being afraid can often be a symptom.

If she checks out fine then you can start working on her 'outdoor fear'. It doesn't make sense that whatever scared her at the house is also affecting her at the the farms.

Why type dog is she?

My dog did exactly the same thing one night. Much later I reflected that at the time he had been tied out temporarily in my parents' yard (was basically an indoor-outdoor dog)and at that particular time my father was out looking at stars with some telescope gadget he'd just gotten. The telescope made beeping noises as he zeroed it in or something. My dog made a beeline for under the bed the minute I let him in. He was such a smart dog that I think he couldn't figure out what was going on "out there in the dark" and that really frightened him. I wish I had been smarter that night and taken him calmly back out to just hang around with me and the telescope because from then on it seems he just developed a variety of phobias that I couldn't figure out how to cure. I think you would be wise to work on the fear of the dark thing; maybe take long delightful walks with her that she learns to love? Good luck.

I recommend a vet trip first, just to rule out any physical problems - my dogs behavior changes dramatally when he is in pain *he had a botched surgery on his right rear leg.
Dogs have ultra senstive hearing, she could have heard anything from cloud to cloud thunder off in the distance, to a gun shot. Just to calm her - go get yourself some rescue remedy and dose her in the morning. The rescue remedy might help with her anxiety, so you are able to take her out on a leash in a familar area and help her brain to let go of the fear she once felt. Try not to react to her fear, dont baby her, or ask if she is okay, just ignore the jitters if she has em. If she does not respond well to this, you might need to ask your vet about a stronger anti anxiety medication. Good luck

Speaking from experience it sounds like you have a sound sensitive dog. I want you to try and pay very close attention to how sound effects his behavior. If you hear thunder, watch your dogs's reactions with out the dog seeing you zoom in on him. Do the same thing when you hear any high pitch bird noises, gun shots etc. even ice makers, wind chimes and or whistles from football games, stuff like that. Than once you get a reaction discuss the incidences with your vet. It's important you do this because building a dogs confidence is different than making it face it's fears. You have to get a handle on the triggers, and to what degree of fear the dog is dealing with will depend on how you deal.