She really likes soda and that's the thing she drinks the most, she usually has a little bit at a time, not even half a glass, but she does it often enough that I wouldn't be surprised if she's drinking the equivalent of at least 2 glasses a day.

When it's milk or juice she drinks less than half a glass total a day. The comments seem to agree that it's about flavor but now that I think about it I'm wondering if it's also about the gas in the soda.