It sounds like you did everything you are supposed to. If you closed all windows and turned off the lights at the intercom the stewardess should come out of the toilet and go back to her seat. Now you should be able to use the glowing costume.
Do you have a recent savegame so you can try those last steps again?
Well, there is a way to stall her a bit longer. I was assuming this was a bug, but now it dawns on me that you forgot to do something to make unclogging the toilet harder for her...
You need to make sure she doesn't have a toilet plunger when the toilet is clogged. You need to get rid of that toilet plunger for good!
