Golden retriever Question

Here’s a question from Becky , please help her if you know the answer reply it via comment coloumn.

I have a 2 year old golden retriever that I got when she was about 1
year old. she is very timid but is a very loving dog. I think that the
previous owners treated her well but she seems to be afraid of a lot of
situations. the worst is when it gets dark. we live on a farm and as
soon as the sun goes down she barks all night. when we got her she was an
outside dog. however after the first 2 weeks of staying awake all night
we finally started to bring her in the house to sleep at night. we
really are trying to break her of this habit as we are currently living in
a holiday trailer, while we build a house, and she can’t come inside
at night. what is she afraid of and should we be concerned? we have
found that as long as she goes in her dog house at night and we put a
blanket over the door she can’t see out and the barking stops. yet even when
she is outside she seems to be barking at nothing. what is she afraid
of and how do we get her to stop barking at night - we really need
to get some sleep. please help me …. your advice is appreciated.
thank you.