Kairi is too sweet to be the jealous type
She would tell Strelitzia,
"This spiky-haired cuteboy is mine (points at Sora), but you can keep the other one (points at Ven)", and then everybody is happy.
Now, if we really want to get her involved in a catfight, we need more mischievous and dangerous opponent. I recently stumbled upon a hilarious piece of fan art. Unfortunately, I don't think linking to that kind of content is allowed, but it is Yuffie telling Sora to
"Think of this as an adventure" while riding his... well, you know what I mean. I think that would be a bit too much even for Kairi.