It's funny that you posted that link, because that is one of the links I read last night. I ended up using vinegar instead because I had it on hand. I think I will get some tea tree oil today. The mold was very, very minimal - just on the wettest part of the wall board at the bottom. We cut it out, but we want to spray everything down just for good measure in case there are roots we're not seeing.
Everything is drying out. It was pretty clear when we pulled the washer out that the drain pipe had been over-flowing based on where the water was. We'll run the water in the bathroom (on the other side of the wall) to make sure nothing is leaking there now that we have the wall open to the pipes. And we'll clean out the drain pipe. We'll test it again before we board the wall back up.
As you said we are crossing our fingers that the floor will dry out quickly. We took off the baseboard in the hallway and are using paper towels to wick away the water and moisture in the gap between the wall and the floor. They had already stopped becoming wet last night. We did realize that the water spread under the floor toward the hallway a little more than we thought, so it also got under the cork floor in our kitchen (where the washing machine sits). That's on the other side of the wall from our hallway.
Thanks, again, for your help and quick replies!