Tbh there is something extremely shady about some of these FF abilities, but this isn't a CRT, so
From what I gather, most of Kefka's arguments boil down to Subjective Reality doing something that she somehow can't handle. If Kefka goes for some blatant hax off rip, that should murderize Kafka (although I do subscribe to the idea that she resists the burning and freeze, but let's shelve that for now as his hax list is large enough that one of these should work on her, I would assume)
Kafka, on the other hand, even if she was TRYING to toy around, probably 1 shots if she lands a single hit. And if I understand right, her Mind Manip goes unresisted.
Seeing as both parties have prior knowledge on abilities, but not on stats;
Kefka seems to have a tendency to mess with his enemy. If he goes in for a physical encounter, he blatantly loses with her sheer advantage. If he goes for his clone summoning, that's probably his best move, but even if we assume that it's something he can do very fast...
Kafka has two wincons, if she gets a hit off she wins. If Kefka makes it so she'll have trouble doing that, she can just use her Mind Hax and at that point it's easy for her to make him stay in place and let her hit him, for instance.
If Kefka DID go for something broken that she doesn't resist as soon as the fight began, maybe he can win. But this doesn't seem in character. Kafka, on the other hand, should have no qualms with winning this fight in the most efficient way possible- That most likely means not letting him get too far away before she casts her mind manip, or just one shotting him if he decides to get close. My vote goes to Kafka, mainly because Kefka seems unlikely to try as hard as her for the win.