Is it at all possible to get her involved in herding? Perhaps take her to someone once a week for fun? Our dogs are always happiest doing what they're bred for, it helps build their confidence and their behavior improves considerably. My husband raises Black Mouth Curs and they can be awful if they don't get to go to work. If they think there's a chance they're going, I can't get them to eat their food, they'll just wait at the door intently!
At one point I was living in an apartment (not by choice) with my Lab mix and Bloodhound. The Bloodhound took it pretty well (but they are not apartment dogs!!!), the Lab did not. She turned from a very good dog into a chewing menace, eating the sofa and rugs. I just could not be mad at her, it was a sign of her unhappiness and I felt terrible. I got them both involved in Search and Rescue, and she absolutely loves it. Her whole demeanour changes when she gets to do 'her job'. Swimming is also very fulfilling for her. She's a real busybody, but a lot more relaxed when she gets to use her brain as well as run.
We now have another Bloodhound that we got specifically for SAR. She's a very sweet dog, sometimes skittish and shy, but she loves to trail. Her body language changes and you can really see the pride she has when she does well. She carries her tail higher, and is just a lot more confident.
We also have a German Shorthair (it's a zoo here!). He was in the pound from 3 or 4 months of age until I bailed him out at 9 months. He is also quite shy, but he loves to hunt birds. The first time we took him quail hunting was amazing. He pointed, retrieved (he won't fetch a toy!), and handed us the birds very gently.
I have seen several episodes of the Dog Whisperer where he rehabilitates dogs by involving them in something that they were bred to do. I'm not saying your new dog needs rehabilitating, but it really does seem to make them happier. It allows them to act instinctively and seems to help them relax. You can also give them a task that is their task alone, it doesn't have to be anything elaborate, and praise the hell out of them when they do well. It can really be anything, from bringing in the chickens to fetching the newspaper, or just going with you to get the mail every day. They also seem to thrive on the one-on-one time.
BTW I think it's great that you've 'rescued' her. Dogs can get so depressed if they feel like they're bad and don't have the opportunity to be good.