Brice wrote the song with Liz Rose, who also has co-penned several of Taylor Swift's hits. Rose told Taste of Country
that the idea for the song came after the two began talking about how "females[…] have our crazy moments". She added, regarding the opening stanza, "I know I've had those relationships on both sides, where you wanted to tell somebody[…]'Why don't you just chill? I'm not going anywhere!" Brice paid tribute to his co-writer in the same interview: "The way she writes and the way I like to write, we just kind of dove in," says Brice of writing the 'Crazy Girl' lyrics. "That melody just took us to a place. It was kind of a sensitive kind of song, but it still had this edge to it that was really cool. We just went for it.
It was one of those days that seems like it just flew by," he continued. "It was just a couple of hours that it took for us to write that song. Sometimes songs that sound that simple, sometimes those are the hardest to write. It wasn't. That one came together really sweet that day. Magic was in the air."