It doesn't make any difference if they had sex that day or not, and because of the naked photos I think it's pretty safe to assume that they did. Sex is the only thing Jodi had in her arsenal to have him pay even one bit of attention to her after the break up, and like so many women have believed before and always will, Jodi believed she could convince him to get back with her with offering him sex.
Whether or not they had sex before she killed him is immaterial to the case, and given the photo evidence they very likely did.
I think her strategy was the same as it always was but this time telling him she'd moved on, and this was just "for old time's sake" sort of like "good bye. let's be just friends" sex. But Jodi's real plan was the same as it always was - win him back to her with sex. Except this time she was prepared to either make him dump the other woman from the Cancun trip and take her or she was going to kill him.
She was never satisfied with the occasional sex romp with him, and was pissed off that it was not working in getting him back to her, so she put her foot down and decided either he take her back or she'd kill him. There was no way she was going to allow anyone but her to have him. If she couldn't have him then she was going to make him pay for that with his life which conveniently also would keep anyone else from ever having him. A story as old as time itself.