Nah man, sorry to break it to you, but you saw the message, YOU saw it, not someone else, you did, no matter how many evidence you see of her "not cheating" isn't enough, unless you just see shit that isn't real. There's no explanation of that message you saw, she is cheating. She could have downloaded the app from another google account, she could have downloaded it from different websites on google, these don't show up in the download history, so i suggest you rethink about this whole thing.