Ok, so lots of food for thought:
paulaplumpbottom gorionin
yes, she didn't have the receipt, but it's one of those shops where they will let you exchange without one. Probably not give you a refund, but exchange, deffo.
pyjama I did not have the receipt on me, so no, did not offer it at the time. Probably can't find the receipt now anyway, because it was ages ago.
jamieandhismagictorch no, she def expects me to exchange it and send her a bigger size, because we discussed what size to get etc. You see, her DC has just turned 13 and I got age 13 - 14. When she mentioned it and it was clear she wanted me to get a bigger size, I said, I think age 13 - 14 is the biggest size they do in children's so she sort of said, oh, well can you get a refund and get something else.
spidermama I honestly don't resent buying for her children, I enjoy trying to find something they will like. I just feel a bit at this situation, but it is rreally not a AIBU by stealth in that I think I should not even have to buy the gift in the first place.
tracybath I feel like you: I was brought up to say, thanks alot, it's lovely even if it is hideous AND doesn't fit!
Thing is, she could always re-gift it, as she presumably knows lots of kids her DC's age, so it wouldn't be complicated for her to do something with the tee, even if she
couldn't be bothered didn't have time to return the thing, it wouldn't need to sit in a cupboard forever.
(runs away having opened the can of worms that is regifting)
FWIW, the reason I did not enclose the receipt in the first place is that the shop in question does 'gift receipts' but I was buying about 12 items and the cashier said it would not be possible to do 12 separate gift receipts, or rather she could but it would take ages, so i just got a normal receipt.
Maybe i am being a bit u. Dunno.