I'm more than a little nervous about letting them see each other.
Since they'll be in different rooms, I can probably swap them over for a few hours, so that they get used to the smell of each other. This is probably more important for Kai, since he's far bigger than her, and kittens are going to be naturally expecting to have to learn to interact with other cats, so I don't think she'll necessarily have a problem with him.
Since he's already more than a little shell shocked by everything, and I suspect she will be after a 2½ / 3 hour car journey, hopefully they won't see too much of a threat from the other cat, and will just be happy that there is someone else feline to interact with.
I will not leave them together, until I'm absolutely certain that he won't try and harm her, and even then in a situation where she can run and hide in places that he can't get too. Even the most patient and friendly cat will have off days, when a kitten could be annoying to them.