[ All of the suggestions presented seem to be pretty solid, but which one should they rely on? Using the dust when it might not be needed would be a waste of valuable resources and she's not sure if she wants to ask that of strangers. ]

We don't know what the daily habits of those inside are like. [ So in short it's difficult to tell if they would ignore the cat flap moving idly or if they would notice a window. ]

Having more than one way to get in provides us with more than one way to get out.