After my sister held a newborn kitten, the mom started attac

  Why?
You should, more than anything, tell anyone also who try to hold the kitten to be careful from now on. The mother is trying to train the kitten in self-defense. Lions sometimes shove their young off cliffs to make them stronger.
since its a newborn some mother cats get freaked out if the kittens are handled because you leave your smells on it and the mother doesnt like it because it doesnt smell like her kitten and usually when this is the case the mother will kill the kitten. it is very sad but that is how some cats are.i would suggest not handleing the kittens as much as you can in the first 2 weeks of life. if you have to move the kitten wrap it in a wash cloth or something so that you dont rub your scent on it. i hope your kitten is ok.
.......... and this surprised everybody, how? The mother cat is rejecting the kitten because it has a foreign scent on it. Just keep reintroducing the kitten and she may stop - if she doesn't you will have to hand rear the kitten yourselves.

Mess with Mother Nature and she messes you right back.
Your not suppost to touch them because the mom will reject it. Since it doesn't smell like her. Moms hide for a reason and you shouldn't touch them for a while.
You can't touch a new born cause your scent would be on it and it won't smell like its mother so it wouldn't care for it or It would kill. Try you best not to touch them until they're old enough.
Apparently it didn't smell like her kitten. I had heard of this, but I didn't think it really happened. Is the kitten okay?
DONT PICK UP NEWBORN KITTENS! Everyone knows this! The scent will smell like you and she will think that the arent hers!