a BB gun on low power won't penetrate either, but I was warned by the LEO NOT to shoot them with a bb gun just to pop them and run them off, it's considered cruelty, and does carry a fine. Just passing on what I was told. I would bet the mortgage if you ask animal control or an LEO they'll tell you the same applies to your rat shot.....
as for putting your broody back with the flock, here's what happened when I did it last year. I left the chicks in the separated part of my coop and run. She about went NUTS trying to get to them, so I moved them to my stock tank brooder under the carport for a couple weeks and let her forget about them. She had no problems going back to the flock, but I'd say if she can see or hear the chicks, she'll go nutso trying to find/get to them....