My mum and dad used to help out when my kids were at school they always bought there summer sandals , and winter school coats and shoes, one of my children earns very good money and has no need for help but the other two aren't so well off, they don't ask but I m honoured to be in the position where I can offer
I think there may have been a misunderstanding and your daughter thought it was a general annual offer and you rightly felt prickly that she had presumed
If you know it's a bit of a struggle then buy them and be glad you know what sort and what size, If you know your daughter can well afford them tell her that you feel she's jumped the gun a bit and while your happy to help out she needs to make more of an effort to discuss ithese things with you I m thinking some pride and 'not losing face' is getting in the way of your relationship