Emmaline
Hippety Hop!
Might backfire on her, though. Be careful.
Good point Mel if it's something of a stinging nature.
Once you spray it can you tape something over it in case whatever is in there comes into the room?
The vent itself is only an inch or so wide at the most and on the outside of the window frame so I don't think that will be a problem as long as the window is closed immediately afterwards.