Hi again,
I know exactly haow you feel and after hearing a little more about her she sounds very similar to a retriever bitch I met while I was working at Guide Dogs for the Blnd. She was also on the small side, although a deep red in colour. We had her litter sister at the same time and they both displayed a scary obsession with water! I'm not talking your normal retriever love of the stuff, they would sit by outside taps and stare intently at them to the point that food was ignored, the taps were not running or dripping! Water buckets in outside runs were defended by this bitch as she stood with her front feet in the bucket. If left alone she would then dig in the water.
In the house she was the most loving and obediant little thing a real treasure. She, like your bitch, had a very large dollop of retriever stubborness in her and would only work for some people.
On top of this she was a nervous dog and displayed much of the behavior your bitch does. She was rejected from the training programme and rehomed. This was a massive failure as she just couldn't cope with the change from kennels. She did bite out of fear and although the family was very understanding it totally screwed the dog up and she then couldn't cope with coming back into kennels. We did everything you could possibly think of and in the end a member of staff took her on as a pet. This person was an angel and went to hell and back with the dog. In the end the dog's quality of life was so bad she had to soul search. Last I heard the dog had bitten two other people but she was still alive. Her litter sister never displayed any nervousness although she was unsuitable as a guide due to her extreme obsession with water and has made an excellent family pet.
You could try an intensive training strategy. The dog does not move off it's bed unless under your direction. Teach her to find and retrieve a toy hidden in the room and she gets a treat as a reward. Start with the toy where she can it and then when she can do that hide it. Only teach her and not your other dog. This is time and energy intensive but giving her fun and direction may take her mind off everything being so spooky. Intersperse games with some serious obediance commands for both dogs and reward both. Over a few weeks lengthen the time she spends on her bed gradually. The idea being that she is busy and has things to think about and the command to go bed and stay are just part of the game. This will use her mental energy in a positive way and her mind will not be ticking over on her own imagined threats so much.
Like I say it takes up your whole life for a few weeks, get your daughter to do some of the games and obedience, with food rewards.
Hard work but if you think it sounds right for her then it's woth a try.
Sorry to go on but I just wanted you to know that I understand she isn't the devil dog from hell and that you love her - I've been there and it is so hard!