Personally, the mother of said 15yr old was very rude in sending you a message like that, and I’m damn sure I would have let her have it from me. If said 15yr old couldn’t say something to you personally, like next time grandma can you please not purchase clothing for me. Simple but at the same time, I wouldn’t be giving any gift card or voucher and your daughter would only get a fb message merry Christmas. There were the days my mother insisted every birthday she would send me a slip (petticoat), something I have never worn since I left home. Each year I would just say Thankyou, bite my tongue but would send it back to her for her birthday or Christmas and she was none the wiser. Mind you it did stop when she got dementia, she had forgotten who I was. I laugh at that, but I do live on the other side of the country and don’t get back very often.