One of my kids left a leaking sippy cup of water tipped over on the hardwood floor. This has happened a ton of times with no damage, but this time, the leak just happened to fall right on a seam, and I just happened to not notice it for a while, so the cup leaked almost all its contents. We have random-width tongue and groove pine flooring that's about 3/4" thick. The edge of the board where the leak was has swelled up maybe 1/16" higher than the board next to it, leaving a sharp ridge that sort of trips you. Of course this would happen right in the middle of the entrance to the kitchen, not in some out-of-the-way low traffic spot.

Anyone know if it's possible to flatten this ridge somehow, or if it will dry out over time? I made a little tent out of a plastic drop cloth and put a dehumidifier under it in the hope of drying out the wood, but I'm not sure that's going to help. Any other suggestions?

Give it a little time, a month or two and see if it goes down. It will probably go back down but not all the way. You may still have a small raise even after the wood has dried.