AITA for telling my sister what I read in her notebook after she left it open in my kitchen?

The first sentence I saw was my name. I read the next three pages.

My sister had left her notebook open on the kitchen counter after staying with me overnight. I initially thought it was the recipe notebook she carries around. Once I read the first paragraph, I knew it was something private. I kept reading because it described how she sometimes finds me exhausting.

When she came back for it, I said, "If you think I turn every conversation into a competition, you could tell me to my face."

She looked at the notebook and asked how much I'd read. I told her. She said the pages were her working through a bad evening, not a message she'd chosen to send me. I said leaving it open in a shared kitchen made it hard not to see.

That's true of the first line. It isn't true of the rest. I wanted to know what else she thought.

She has apologized for one specific remark from the evening we'd argued about, but refuses to discuss the notebook paragraph by paragraph. I keep thinking that if she wrote those things, they matter even if I wasn't meant to read them.

She says I took both her privacy and her chance to decide how to talk to me. AITA for raising what I found rather than pretending I hadn't seen it?