Why is Amity here? Even if Amity did decide to snoop on Luz’s phone, it’s not like that

Why is Amity here? Even if Amity did decide to snoop on Luz’s phone, it’s not like that would have revealed what Luz is up to. Luz left their phone behind before even they knew they were going to attack the parade. They didn’t tell anyone else the plan. I feel like I’m missing something here.