As Aaron pled out in his case regarding Kayla no evidence was put on the record.
He did plead out, but he also immediately did a stream after his plea deal where he literally admitting to doing everything he was accused of. That's able to be used against him.
Could the best defense against Kayla be that she posed willingly, or as a mitigating factor?
No. It would change some of the narrative around the picture's spread that it was a sneak picture done without her knowledge (it's not done without her knowledge if she looks into the camera and poses for it, obviously) that Nick has been trying to spread, but the legal issue is that Aaron wasn't given permission to share it out (that we know of). There are exactly two defenses that I can think of that would help Aaron:
1. "I didn't do it" (and then make the State prove it)
2. "I did do it, but here's where she gave me permission so I committed no crime" (and then provide evidence)
Aaron already admitted to it, so 1 is out of the question. If 2 was applicable, he could've given it to his attorney, who could provide it to law enforcement and presumably get the charges dropped. If he hasn't done 2, it's because he can't, because he doesn't have anything to show he was given permission to do it.
He never got an Alford plea/pled no contest, so his plea deal could be used against him in a civil court. He also literally admitted to it, so even if he were to withdraw his guilty plea and decide to attempt a trial, his admission on live stream can still be used against him. He chose the absolute worst possible option at every opportunity to protect himself legally, and you should not try to even attempt to come up with a legal defense, because he has none at this point. And the reason he doesn't is because he destroyed it himself, because he's a fucking retard.
He thought "Once I plead guilty, I can move on", but was only able to do so by conveniently ignoring the dozens of people who warned him explicitly and unambiguously on multiple occasions with 100% consistency that if you plead guilty, Nick will go after you with the intent to destroy you, with absolutely no remorse, because he's already decided you deserve to suffer and die. Everything that Nick tries to do to him legally was avoidable, and he chose not to avoid it, because he's a fucking retard. If he can somehow get an HRO against Nick (who, as Potentially Criminal pointed out, is married to the victim of his revenge porn case, and therefore has at least a decent chance of having it tossed just because of that alone) it'll be in spite of the fact he's a fucking idiot and because Nick is a legal failure in every sense of the word, not because Aaron's a sympathetic victim with zero obvious issues that would warrant a legal layup.
Melton deserves to be thrown into a woodchipper and not just have a RO against him, but his creepy fucking behavior spanning years was always going to be less problematic for a court to decide he deserves to be restrained: and if they somehow decide that Aaron's daughter can't have an RO against Melton because of her dad, fucking nuke that shithole state. They already deserve it, but it deserves it several times more anyways.