Actually, no. She is drinking a mix of water and yogurt.
It is a beloved, typical summer drink in Bulgaria and Katie is addicted to it. You can find a similar thing in India, called lassi and while we only put salt in ours (not in Katie’s), I’ve tried both salty and sweet lassi with a variety of unexpected spices, like cumin for example.
At home we call it airian (or aryan) and it is the most refreshing drink you can get in summer (beats all the sugary sodas and tasteless vitamin water drinks). A lot cheaper and healthier too.
If you want to try the bulgarian version, just pour equal parts yogurt and water and a teaspoon salt. You can add more water if you feel it is too thick for your taste. And if you feel adventurous, here are a few lassi recipes that I like:
Mango Lassi (you can change the mango with any other fruit you like, but this is one I enjoy in particular. You can also add cinnamon)