Always pick up the bill, with one clear exception

Fabrizio Rausa is direct on this: pick up the bill. Whether she orders a water, a coffee, or a drink, you pay. You will never be worse off for doing it. The one exception is when you can clearly see she is using you, for example if she is ordering the most expensive items on the menu and it is obvious the interest is transactional. In that case, use your judgment. But as a general rule, pay like a man and do not overthink it.