I'm with the shop on this. It's pure laziness to go out shopping in your nightwear. Unless you've only got one arm or no arms at all, it takes all of a couple of minutes to pull on a jumper/T-shirt & either a skirt or a pair of trousers/track bottoms. It shows the standards of some of the community that the store felt it necessary to put up notices in the first place. As for that woman wittering about how difficult it is to get three children ready in the morning - get up earlier!! If she thinks boycotting the shop is going to mean anything to them, she can think again. Does she really think they can't do without her pyjama-clad (& probably unwashed) self trooping among the shelves? It's a shop, not a venue for a sleepover.
The headmaster has my support too. What on earth makes people (& it's apparently mainly women) think that it's OK to turn up at the school like that? How hard can it be to get dressed? They just can't be bothered. If you don't show you've got standards, people have no reason to think you've got any.