She looks like a buff brahma to me. She's about 1/3 the size I would expect at this point based on your photos. Genetics are interesting and I wouldn't say dwarfism as it isn't really how it presents in birds quite like this but a defect definitely. It might be ok if it's already made it a month. But it might not live long/ever be too normal. I will be interested to see how things go, do let us know.
but I should show you our littlest runt, I think the other 2 will catch up but this guy is like you said 1/4 of the size. I thought he would grow, even added some high protine feed to his feeder but still just so little, I put the 3 little ones and two pullets I haven't decided what to do with yet in with my keepers. Seems completely fine accept so tiny. I always wonder what's wrong that makes them so tiny. But our goal is to hatch about 100 here this year so we were bound to get a tiny guy. Cute though. We will probably end up keeping it around at least until we know girl or boy. Good luck to you!