Piper told Emma she had a father who is never coming back. Plus you could read into that visit scene of the connection of an older sibling. Also her always being in the coffee shop keeping an eye on Emma. I mean it's perfect really. She knows what she's doing and where she is at all times. She also had no problem with giving the info about the Mayor to the Sheriff. And as possibly insane as Piper might be, she's manipulating Brooke who's not really insane, but still not the most moral person in the world, knew about Branson's past for a future frame up and made Brooke get close to Branson but eventually she grew feelings for him, so when/if she planted that evidence her confronting Branson was genuine emotion and hating the fact that she set up someone she has actual feelings for, which is something not much people have given to her despite the immoral nature of it all. Piper makes the most sense in terms of being on the outside and out of town, and crafted her new identity in the form of a podcaster who podcasts about murder cases. A lot of it adds up.
I'm afraid worst case scenario, they're playing on the expectation that people haven't seen the Scream films and will rehash and recycle previous tropes such as Jake being such an obvious suspect and turns out to be the killer. I hope not as they seem to have the films in mind at times for certain call backs but that could go either way. Despite my Piper/Brooke theory, Audrey, Hud and Kieron are still suspicious to me. If Jake is one of the killer's I'll be really disappointed. You could interpret Jake not dying as either him doing it himself or possibly the killer keeping him alive because they need him for something at a later point.