I guess when the assailant ran up and started unbuckling the kid the confusion probably gave her enough time to sort the buckle - With something that unexpected it would probably take many a moment to realise what is happening, then a moment longer to try and reason with the assailant without realising quite the extent of the issue. As for self defence, to pull a gun and shoot the assailant will to some seem out of scale - the assailant having no weapon in the attack - but at the same time if someone attacks an infant, I personally would fully agree with pulling a gun and defending yourself and your family to the fullest. The fact that the attacker was obviously delusional and suffering from mental problems? Sure that does give some 'excuse' for the behaviour in that she wasn't in full and capable control of herself, but out on the streets when being attacked you don't exactly have time to stop, consider the mental state of your attacker, phone the police and social services, get the person checked out and dealt with in whichever ways are needed (drugs, counselling, institutions, etc...). That person is an immediate threat and needs dealt with. Had they pulled a gun, whatever the mental state, I doubt anyone would have much concerns over shooting them considering the immediate danger everyone in the surroundings would be under. As for the shop owner who refused them entry - utter, utter scum. Sure he may not want people barging into his store and smashing the place up, but there is a massive difference between gangs fighting and a mother with baby being attacked. If I had my way he would face some serious consequences - if anything he was an assistant in the attack in refusing to help stop it.