Lack of history is not always a bad thing. I volunteer heavily in a GSD rescue near me, and we don't always know the dogs history. However, we ALWAYS know the dog. We do a thorough evaluation. I go there (almost) daily to do basic training and exercise with the dogs. I know every rescue is different, of course. But, I think, most rescues really work hard to match the family to the dog. We want that second home for the dog to be a forever home. So, we're really OCD, almost, about perfect placement.
I think being skittish/shy is not necessarily a bad thing. It could be the dog's nature. But, it could also be the fact that the dog is 1. in a new environment, 2. meeting new people, 3. is a rescue.
There will definitely be an adjustment period of a few weeks when the dog goes home with you. She may have accidents in the house, may be even more shy and skittish, may be afraid to go into certain areas of the house, may forget some basic commands, etc. This is all fairly normal in an adjustment period.
I would worry about taking a highly anxious dog into a home with children. But, if she's shy - that's different.
How long ago was she in that foster home? Are we talking a matter of a few months ago? Or years? People who foster dogs wouldn't lie about her being OK with kids. So ... if she just left that home a few months ago - I'd be OK with taking her in.
First special delivery - April 2010 :