I was very worried and tried to calm her down by sweet talking her to open the door; "It's okay, honey. I'm right here. You need to unlock the door, okay? That way we can get you out and you can come out and we can play a game! Do you want to play a game with me? Great! I want to play a game with you! Just come over to the door. See the handle? Can you turn the knob on the handle? I know you can do it!"
She informed me she couldn't get to the door because there was a spider on the stool. "Do you see a bath toy? Can you squish the tiny spider with a big bath toy?" But she informed she was afraid of spiders. Actually, at that point I was very impressed with her composure. If I was stuck in a small room with a spider, I would be in hysterics.
So I tried a different route. "Can you push the stool over by the bathtub? Great job! I knew you could do it! You are amazing! Now, come stand by the door! Are you by the door! Great! Now touch the handle! Don't worry, you are doing great! We'll get you out in just a little bit!" After about five minutes of sweet talking and gentle coaxing, we were no closer to getting her out. Drek walked over to the door and said in a stern/angry voice "If you don't unlock that door right now you'll be stuck in there forever."
Two seconds later I heard the door click and our niece walked out.