You want to be treated with respect & like you matter to them. Everybody wants that.

This person isn’t treating you like that. For some reason, this is how they act. You are frustrating yourself “expecting” something from someone who does not give that to you.

It is causing you a lot of anxiety when you set yourself up for the waiting for a response from this friend. You don’t have to do that to yourself. That is having a boundary.

Since you know this friend gives you the stalling tactic you can; not ask her to do anything anymore, or ask other friends while she is thinking about it. Then when/if she finally responds to you, you can say someone else is going with you and she can join you both or not.

You can’t make her stop doing what she does. It is easier to acknowledge who she is and adjust yourself.