I think you did a great job setting an emotional boundary with your friend, because you were very explicit, when you told her that you can't respond to every single email that she sends you multiple times a day abut the same thing, because you need to focus on other people and your other relationships too, which have equal importance.

Now, if she tries to guilt trip you or shame you b/c you set this boundary, then that is your evidence that your boundary worked. If she ignores your boundary and continues to be demanding, then just repeat your boundary with her until she accepts it. If she refuses, then you need to decide if she is someone you actually need in your life.

You can also set intellectual boundaries with her via email, when she will object to your emotional boundary with this phrase (or something similar), "I understand what you're saying. I just don't agree with you. I don't mind if you disagree with me, but please don't insult me."

Don't give in to her demands or respond to her attention-seeking behavior. Just ignore her emails. You can also block her email address. It's up to you.