If it was me I would not have opened my front door if I heard a commotion outside, I would've just rang the police, the childs mother opened the door to see what was going on. Maybe if she had a licensed gun she could've used it in self defense. Here we are allowed to use self defense in other ways, as long as it's reasonable and not over the top, for instance I knew a case of a guy who was in bed early one evening as he had to be up early for work, he woke in the early hours with an intruder stood over him with a crowbar, the guy in bed jumped up and reached for an item to whack the guy with, so after a struggle the guy whacked the intruder over the head and sent him flying down the stairs, the guy claimed self defense and that he'd used reasonable force, the courts convicted the intruder and sent him to prison, he also had to have surgery on his back as the fall down the stairs damaged his spine. So although we can't have guns here we can use whatever is available to protect ourselves if under attack.
Quite a few people modify their guns, but a smaller number make their own guns from parts. A select few make them form scratch, but that requires skills and equipment that most don't have. These guys and gals were given a box of parts and expected to assemble a working firearm within 3 hours.
I think I seen actor Alec Baldwin's name brought up in this thread? Anyway, it's in the news today that him and the armorer, on the set of filming the Western "Rust" will be charged with involuntary manslaughter for the death of the cinematographer on the set.