To be honest, I can't see the need to bring a Shetland indoors at night. Indoor lambing has its own associated problems, Id just let her get on with it.
I don't know anything about GFDs, but I am starting to notice the proliferation of threads on here about how they wont mother or need assistance lambing or.....
This could, of course, be because lots of people have them on here or they are not an easy breed to keep for whatever reason.