OK so I am going to bring my random ramblings back to life. I've been thinking that it's way too obvious that Katie was a red herring and that Shiela is the shooter. That's BS! I have 2 therioes about what actually happened.
1) Katie has a split personality and her alter ego is the shooter. That would explain her victim/aggressor behaviour. If the writers were creative enough to write this I think it would be gold! And give HT some really meaty material that actually makes sense!
2) Ivy is the shooter. Ivy has always had a dark side and she has a motive. Quinn knocked her into the really nasty river in Paris and outed her to Wyatt about still being in love with Liam.
I really like #2