sometimes the younger child eats better because they want to do what the older one does so drinking from the same cup or using the same cutlery is normal, my son was a picky eater until he started sitting at the table with his dad and then he wanted to try the same food his dad had, i think this is normal and it is how kids learn, as for germs they would pass them back and forth as they play or cuddle, no point in an argument, just because you would not do it does not mean it is wrong, let your daughter parent the way she wants, in the end it is nothing to do with you.