Is there any part in the 7th book where it is detailed of who personally killed Ariana Dumbledore from the trio's duel?
“And there was an argument . . . and I pulled out my wand, and he pulled out his, and I had the Cruciatus Curse used on me by my brother’s best friend — and Albus was trying to stop him, and then
all three of us were dueling, and the flashing lights and the bangs set her off, she couldn’t stand it —” The color was draining from Aberforth’s face as though he had suffered a mortal wound. “— and I think she wanted to help, but she didn’t really know what she was doing, and I don’t know which of us did it, it could have been any of us — and she was dead.”
Harry Potter and the Deathly Hallows Chapter 28 Missing Mirror
I don't quite remember if it was mentioned in the books.