Harry was in a terrible mood. Not depressed, of course, but angry and frustrated, two difficult emotions for him to navigate. He wanted to seek out Draco, but he didn't really want to bring those two feelings into his fledgling relationship. So he took to wandering in the very opposite direction of the dungeons for a change. He didn't want to go to the hospital. If Seamus was hurt badly, the last thing he needed was an argument, which Harry was sure to give him at the moment.
That was when he noticed the wooden clatter of what was surely a wand hitting the stone floor. It seemed to be coming from the Astronomy Tower, which he was just wandering by at that moment. A wand dropping on the floor was rarely a good sign, so he took himself up the stairs without hesitation. He spotted the wand on one of the stairs and picked it up, at the same moment he heard sniffling. Another bad sign.
At the top of the landing he spotted Ava. He'd only just been talking to her on the journals, and she seemed to be in a fairly unhappy mood, but he didn't know she was going to find her crying. "Oh," he said, announcing his presence. "Sorry, I heard..." He stepped forward and handed her back her wand, handle end first. "I didn't mean to intrude," he added, lingering a moment to see if she wanted him to leave or stay.