It will be hard. And Im not sure I was very persuasive, its just an interesting counterfactual.
The only defense I could imagine is the one I mentioned, where Charlie's defense theory is that Magbanua/Garcia/Rivera killed Markel as part of some scheme to extort the Adelsons. That theory falls apart on logical (and evidence) grounds rather quickly....but its still not quite as ridiculous as Katie's defense theory in this last trial where Charlie and Garcia hatched the plan behind Katie's back.
Katie has been allowed to represent herself as a sympathetic character to this point whereas she will be the villain in the Charlie Adelson defense. And there's quite a bit to chew on there. For instance, I don't think anyone - neither the prosecution, nor the defense, or even any of us spectators who aren't burdened by admissibility rules - can logically explain how this murder plot was hatched and the reason we can't is because of how deceptive and manipulative Magbanua actually is.
Charlie and Katie start dating at the end of 2013. Charlie and the rest of the Adelsons needs someone to kill Dan Markel. Katie knows some people might be able to pull it off. Katie agrees to help stick-handle the operation and manage the interactions with the killers. Dan Markel is killed and everyone gets paid and then spends money on *advertiser censored* and toys. Charlie and Katie stop seeing each other around Jan/Feb of 2015. Garcia and Katie get back together in May 2015.
But what does Charlie know about Garcia, and what does Garcia know about Charlie? Who did Garcia think he was killing Dan Markel on behalf of? In early July 2014, Garcia tries to run Adelson and Magbanua off the road the day they were trying to go jetskiing. He then calls Harvey Adelson and leaves a nasty voicemail. This is in between the first trip he took to Tallahassee to kill Dan Markel and the second trip to Tallahassee later in July when he actually kills Dan Markel.
The only person that could possibly explain these logical gaps is Katie Magbanua, and if she isn't testifying in the next trial for the Prosecution or the Defense, you can be damn sure Magbanua will be the target for the defense. And she wont have Kawass or Decoste there to sympathize for her.