Brown eggs are hard to candle if you don't have a super powerful light. Some folks buy a powerful LED flashlight that does the trick. I just use the wait and see method on the really dark ones.
Hawks are a predator of opportunity. They don't seem to bother my chickens unless the are super hungry. I think they prefer to have something they can carry off. Several years ago we saw one right after it had killed one of our sex-links. It didn't even get a chance for a bite. It was sitting on the body in the field and we ran it off. The chicken didn't even have blood anywhere. It was pretty amazing. I think the concussion of the hit and claws must have killed her but she wasn't bleeding anywhere. After that the chickens stayed in the run and only free range when we are outside to observe. We have a family of hawks that stay in our area.
As for your singleton, if you brood some babies, you might get her in with the younger group but getting her into the crowd of the older ones might be a challenge. Most likely she thinks of you as Mama or the Alpha now since you have been protecting her.