See the thing is... it was a datamine. No one at IS ever said that she was going to be a free unit. People just assumed. And we all know what happens when you Assume.
If anything, the datamine should've alerted people that something was up. Aside from Camus, Xander and the CYL units, we've never gotten great units for free. The mysteriously absent Arden also should've set off at least a few warning signals.
That said, the fact that neither Arden or Ayra were highlighted in the trailer reeks of purposeful misdirection. If nothing else IS have certainly cost themselves a lot of trust with this.
There's a lesson to be learned here - if you want a unit that is shown in a trailer, save orbs until you know how they're gained. The Sigurd banner is still here and will be for the next 10 days but everyone jumped on it the instant it released and in this case it cost them.
I'm decently entertained by how this entire troll was set up around Arden of all characters. I'm sure that more than a few people will be feeling resentment as that strange, overly-detailed character waddles into their barracks as a trials reward instead of the Ayra they expected.