It’s on you.
Always offer to pay for the drinks, movie tickets, food, etc. She may be insulted by the gesture, what with this whole feminism and girl power thing. But if she’s insulted by a gentlemanly act, that’s her problem, not yours. And this isn’t only for dates. Whenever you’re with a lady, always make it a point to offer to pay. If you’re in a platonic relationship with the hypothetical young lady and you pay for her coffee, she may ask “is this a date?” Your response is up to you. You may want it to be a date. But in keeping with the platonic nature of my relationships, I’ve responded with something like “we don’t have to be on a date for me to be a gentleman.” That usually clears things up…in a muddy sort of way. It may be something that’s more acceptable here in the South, where I live, than in other parts. But even in the South it’s still more or less against the social norms of platonic relationships. It’s one of the social norms I generally disregard, and encourage you to do the same. If you’re in a group and have the budget, offer to pay for the whole party. This isn’t something you need to do every time, but it’s all part of being generous and taking care of people. It is inseparable from the behavior of a gentleman.