Dear teachers, what should I do when I encounter a fool?

A few days ago, I had a big argument with a friend. It was the first time we argued, and it was very intense.
I've known her for about six months, and I didn't expect her to be so selfish.

To briefly share my feelings, my friend always puts her own feelings first and never considers others' feelings.
She only cares about her own comfort and getting what she wants.

In simple terms: I said I would help her with this and that, and she said I didn't ask you to do it. I asked why she didn't mention it when she asked for my help, and she said I could refuse. I told her I was doing it because of what she said, and she responded, "What I say has nothing to do with you? That's your own choice. Even if I said something wrong, you shouldn't have chosen to do it."

It seems like my concessions and understanding are taken for granted. The most I hear is, "I didn't ask you to help me, so what if you helped? If you treat me well, I should treat you the same way."

It's not that she's ungrateful; I feel she simply doesn't see others' efforts. She doesn't see the various sacrifices others make to satisfy her.

Honestly, I don't want to give up this friendship, but I really don't know what to do to maintain a healthy relationship.