I know it's horribly depressing to watch a dog sitting in a corner being terrified when you just want them to be a happy part of the family. We've been through that with our Rox and I had to learn to restrict myself and not hug her all the time but give her the space she needed She'd cower in a corner every time someone raised their voice a little and froze in fear when she was patted. She still has moments when she seems to fall into a deep black hole and often we just can't work out what we've done to trigger such a reaction. But this now happens only occasionally and watching her transform was worth the pain.
Just hang around here and keep on writing about about your questions and her progress. There are a lot of people here who know a lot about dog behaviour and training. I found this forum incredibly helpful working through some of her issues.