To be fair, they have the same range. And the AoE on Zakeru should help loads.
They also have an over 2x AP advantage due to the calc + heavy scaling chain. So I honestly feel a Zakeruga would one shot her.
Jikerudo also takes away basically everything she does. She'll be pinned to the wall since it's made of metal, and unable to do anything, free to be one shot.
Issue is, Gash and Kiyo would have to do this 20 times. And, simply put, Kiyo simply doesn't have it in him to cast that many spells. Gash could go on, but without his spells, he won't be able to reach her, and would only be able to protect Kiyo. Though he'd likely be pretty good at that, given his durable body.
The whole floor on fire thing seems weird when the floor is part metal and part stone, so I highly doubt that would work well, if at all.
Rashirudo is honestly a waste of time unless they're at too far a range for her to attack them from multiple directions. And Kiyo is more than intelligent enough to not waste his time, and manually dodge instead.
Best thing they can do here is use Rauzaraku so Gash and leap up and grab her to try and throw her out of sight. That's pretty much their only win con here.
Other than that, Chelsea takes it because she can rez 20 times. So even though Gash and Kiyo should be more than able to take her down a few times, Kiyo simply doesn't have the heart energy to defeat the same opponent 20 times in a row.
So, I'm definitely leaning towards Chelsea through cheesing out their stamina with her 20x rez. Kiyo might opt for Gash to try to throw her out of sight, but flight makes that more difficult, even though Gash should be able to blitz her with his leap. He'd have to manage to bring her down to throw her.
Actually, I think I'll just side with Chelsea here. Kiyo can't fight for that long.