Bella and Abba are very spoiled. Probably the most spoiled dogs I've ever seen. That being said, they are also very well-behaved, when Kate and Ryan are home with them. They get attention every minute of the day that they are home with them.......... .........It's almost like they've given her TOO MUCH attention, that she doesn't know what to do with herself when they're not with her
Well, that most certainly may be the case. Dogs that are spoiled, too attached to their owners, have owners who are home with them all day (not that they are, but using an example), and dogs who were abandoned or have lived thru shelter life are most likely to have separation anxiety. Do you know if she starts getting anxious before they even leave? There are tricks you can do to get them to think that it's not such a bad thing they are leaving, although in this case I don't know if they would work. Such as the "don't give much attention before leaving or when arriving home" or the "change around the routine before you leave so they don't know you are leaving until right before you do" trick.
Do they have a basement? Or is it a finished basement? What about setting up a doggie area in the garage? They can even set it up so it's not too cold out there. Because if they can't crate her, and she can't be free roaming, there aren't alot of options left. Rescue remedy, by the way is great stuff. So are all of the Bach's line of flower essences. I believe, though that if you use it, you have to continue to use it, not sure about that.
Hope your friends can work this problem thru. A totally destructive dog certainly is a big challenge.