A real relationship is built on top of what I call rules and roles. You begin by establishing that she wants to be in a relationship with you. As you get to know each other you set boundaries and expectations, usually when you actually start the relationship with someone you know already the rules of them are already established. If you don’t know them very well you’ll need to talk about it at some point early on in the relationship.
You are taking on roles and rules without setting expectations for her and so the relationship doesn’t meet your needs. The roles in this case are that you are her ATM and she is a princess who does not have to follow rules. You have not communicated on what you need from her probably because you don’t think she would take you seriously, and you’re probably right in that suspicion.
Rules are required to ensure that both partners are getting what they need out of the relationship. Without rules one person gets used up.
This is not a healthy relationship, and unfortunately, is too far gone that it cannot be repaired. Stop buying her things, you are never going to get what you need out of her. I would suggest to stop talking to her entirely.
Start a relationship with someone who you can establish boundaries and expectations with before you start doing things for them. For me personally, I will buy dinner when we are having dinner together, I’ll buy a few things for them when we go out to the mall together, and gifts on occasions like birthdays. Sometimes I like to surprise them with random gifts.
If she starts asking for more, I simply explain what I will do and won’t do, she can either accept it or leave.