If I were you, I'd try, but the other posters are correct that there is no way to know whether she will accept the chick without trying. Silkies are generally very good brooders and mothers, so I think it's worth a shot. You should know pretty quickly whether she will accept it. I gave my broody some store bought chicks and knew within about 5 minutes that all would be well, and they are dong fine now, a few days later. And I did it around 10 AM, even though the best time is after dark: steal the eggs and slip the chicks in from her back side.
What isn't good for their health is setting eggs that are not going to hatch. They can stay there for months, and they can easily die of starvation. They won't get off the nest to eat and drink much, once a day if you are lucky, and over the long term, that isn't healthy. They typically lose a lot of weight while brooding.
As for leaving her with the others, that is really a personal choice. Some on here feel they should not be separated, that it is best to let the strong survive and write off the weak. Others feel the mama and chicks should be protected from the others, just in case. Frankly, if your flock is not aggressive, I would try them together. In my case, mama and 4 chicks are doing just fine with the other 3 hens in the flock, and they aren't even the same breed. Actually, the mama is the smallest hen, and not high in the pecking order. There is no roo in this flock at present, but there were several when I did the same thing last year, and they also did fine.
I do not own a bator and do not plan to hatch and raise chicks except under a broody, as I feel this is the natural way, and the chicks do better being raised by a mama. Just to let you know that my opinions are slanted this way.
