Your attempt at moral equivalence with the barbarity of the Islamic faith shows a lack of understanding of the role of parents under the Judeo-Christian worldview.
Parents aren’t allowed to kill their children for any reason, but they are given the authority and the requirement to train and discipline the child.
The grandmother wasn’t consulting the Judeo-Christian worldview for guidance - she had an emotional, ego-driven reaction and lashed out. Just like Muslims do, though they take it to greater extremes because they know their Sharia law and culture will back them up. Same human fallibility, same after-the-fact justification for it - just a slightly different code of acceptable responses.