Does Tideturner swapping in Diana let her proc after a showdown started?
A showdown starts at a battlefield. I reveal Tideturner and swap it with Diana, Lunari from my base. Do I still get to proc Diana's effect?

When a showdown begins here, you may pay . If you do, [Predict], then reveal the top card of your Main Deck. If it's a spell, draw it. (To Predict, look at the top card of your Main Deck. You may recycle it.)
Artist: Six More Vodka
Card Set: Unleashed
A showdown starts at a battlefield. I reveal Tideturner and swap it with Diana, Lunari from my base. Do I still get to proc Diana's effect?
During an open showdown my opponent plays Moonfall and moves my Diana, Lunari from base onto that battlefield. Does a new showdown start, and can I trigger Diana's effect?
Can I use Diana's beginning-of-showdown ability if she is not on the battlefield where the showdown begins?
I control Battlefield A with Ravenbloom Student. I move Ravenbloom Student to base, then move Diana back to Battlefield A. Is this a showdown, and can I use Diana's trigger?
I understand Diana, Lunari triggers as soon as a showdown starts, before attackers and defenders are designated. Is her trigger part of the same initial chain as the attack and defend triggers — meaning Diana, attack triggers, and defend triggers all go on the chain together before reactions can be played — or does Diana's trigger resolve first and give priority before attack and defend triggers are even put on the chain?