This kitten may not make it, and that's why mom is ignoring the kitten. She knows something is wrong.
I suggest you gently rub the kitten in a towel or blanket to warm it, then keep it warm with a warm rice sock or warm water bottle wrapped in a towel next to it.
It is probably too weak to suck a bottle, so you would use a 1-2 mL needleless syringe to put 1 drop in the side of its mouth at a time. Let it swallow and breathe and give another drop. Feed the kitten tummy down, head up - like the other kittens feed from mom. A warm kitten digests milk better.