“There’s a mother and her baby, she was tortured by a group of teenagers(?) and they take turns stabbing her as she watches her baby being burned alive and then some time later she gets her revenge and somehow her chest up to waist part of her body is replaced by some robotic sharp scissors thingy and she kills one of the teenagers with it.”
https://www.reddit.com/r/NameThatMovie/comments/18oznnw/comment/kelvk07/?context=3
It’s not Machine Girl (2008).