I'm sorry to hear about your kitten's URI. Unfortunately I don't have any answers for you; hopefully someone else will. I would have suggested a steambath, but you did that already. Maybe try it again, making it as hot as possible and leaving her in the bathroom for longer?
I've read elsewhere (at sites that aren't necessarily reputable) about applying a small amount of Vick's/Baby Vick's on top of the nose, but I DON'T know for sure if that product is cat safe and so I would NOT recommend using it.
It sounds like you plan to take her to the vet tomorrow, which is definitely the right thing to do. She needs an evaluation and presumably antibiotics.
In the meantime, the most important thing is to try to get her to eat and drink as much as possible. I would guess that she is drooling because she is forced to breathe through her mouth since her nose is all clogged up. Cats rely in their acute sense of smell when it comes to eating, but since her nasal passages are blocked (and she's feeling under the weather) it is likely that she will be much less interested in food. Cats should not go more than 24 hours without eating, so please try to ensure that that does not happen. Using stinky foods like tuna (which you wisely did) is a tried and true approach. Warming it up is also beneficial.