It only takes minutes to crawl under a fence and get hit by a car, it doesn't matter if they are out there all day or a few hours. JIMO a really bad idea that I wouldn't chance with my kids, and I live in a good neighborhood too. I'm not casting judgement, that's just my opinion on it. Accidents can always happen, I moniter my kids when they are out, but I've put them out and walked away from the door for a few minutes, it only takes that much time for a disaster to happen, but I would say I definetely decrease the chances of a disaster by not permiting them to be loose in my yard if I'm not home.
Either way, it's Linda's choice. Good luck sorting things out with the girls, glad they are getting on well, even the best of buds have a few blow outs here and there
Just ask my girls!