Include her in daily transactions. When you're making a deposit at the bank or buying groceries, explain what you're doing and why: "I'm giving the cashier money so we can have this food for dinner tonight." Allow her to ask questions so she comes to understand the concept of value exchange.
Use cash when you can. Little kids have a hard time grasping the idea of credit. To them, it looks like you're getting things for free with a magic piece of plastic. Instead, put coins and bills in front of them, and let them help you dole it out. That imparts a lesson about money in concrete terms (and it lets kids practice counting).