Same in our house tonight. Nappy and vest sounds fine. There's not a lot else you can do really! Leave the windows open and the door if you can to get a bit of through breeze. It'll cool down a bit later although prob not to 19 or 20. You must have a lovely, cool house. Ours is boiling!
You can only do you best. We strugle to get below 27-28 at times.
Just a nappy and vest sounds perfect. Perhaps put a sheet over her legs when you go to bed.
What we found is that trying to stop it getting hot in hte first place was a solution. It was hte room that gets all the sun all day - so we closed the curtains through the day to stop the heat getting in. Then open the window in the evening to cool it down further.