Personally, while I am a bit taken back with the fact that she said that to you, I do think that it was wrong of you to assume that water would be fine for her. I think that she should have been given a choice of appropriate drinks. If you did not want the children to have soda then asking her if she wanted, water, milk or juice would have been the way to go. JMO.
Really? I always love these questions because you see how others respond and other households runs. When children visit I don't allow then that much free reign over my home, I'm not horribly strict either but I do have a few rules the same applies for when we are dining out. Honestly, it never for a moment crossed my mind to give her a choice of what to drink, like I said, everyone at our table was drinking water. And perhaps, because I've worked with the teens so long, I have learned to be more direct. About a 1/3 of the boys will come to my house insisting that they hate water and refuse to drink it but most, not all, will leave my home liking water. Only one currently refuses water and, interestedly enough, he is the only one currently with a weight problem too.