If the kid hid the pregnancy with baggy clothes, pried the baby out of her vagina with a pair of scissors, and proceeded to strangle the baby, I'm pretty sure she had a reason for doing so and isn't completely on the line of her just being a suck fuck that needs to be jailed for life.
To me it reeks of desperation and complete and helpless panic. She didn't want a single soul to know if it, felt she had no other way of getting rid of the baby, and went to extreme lengths to make the entire thing stop. We can all sit here all day and say she's a monster, but it seems to me she had absolutely nobody to turn to and felt extremely desperate to make the baby go away. For what reason, I don't know. It's already known that the mother "denied" the pregnancy the entire time, but honestly not doing absolutely anything about it? I understand if your daughter came home preggers one day you're going to be pissed at LEAST a little bit, but how the hell is it logical to deny that she's pregnant then continue to to do nothing afterward?
Let's pretend the mother isn't a fucking psycho. Let's pretend she's one of those parents who doesn't give a fuck what the kids are doing all day and probably doesn't even see them for several days at a time. Let's pretend her daughter came home one day and said "OMG I'M PREGNANT" and the mother, probably in addition to being pissed that she had sex in the first place, blurted out "NO YOU'RE NOT".
What boggles my mind is that right after this exchange the mother still didn't do shit. Really? Did she go back to not giving a fuck what the kid is doing all day? Even if I give her the benefit of the doubt and assume she's one of those mothers who see or care for their children much during the day it still boggles the mind that 1) she managed to be completely oblivious to the pregnancy in the later stages and 2) absolutely failed in any meaningful way to follow up on this initial pregnancy claim.
Any way you look at it there's no way you can't blame the mother on this. A fourteen year old killing a baby in this way is absolutely not normal. More than saying she's psycho and needs to be locked up for the rest of her life, I'm actually more inclined to believe she lived in a pretty damn hostile environment, and she probably was threatened in some way or another if the actually was having a baby. For her to take the matter into her own hands in this gruesome manner shows how desperate she was, and I don't think it's simply because she's batshit insane.