Right... Disillusionment? I forgot about that. But, she will be able to hear the stairs. Kieran did not muffle them, only himself. By the way, I forgot - can you see a disillusioned person's drawn wand?
Could we decide that Kieran caught the tube and that is how she knows he is there? The only other option is that she runs away, and that is a less interesting narrative, I believe. Either way she has thrown it and he will be temporarily blinded.
Well considering that you can't see a person's clothes or any backpacks, etc. that they have on them at the time of casting (plus the wand's actually casting the charm) then I'd say no. But how about Kieran sees the magnesium blow and starts casting on Avia and breaks the charm that way?
If you're reading this you have 5 seconds to...

I can drink in 14 Days, 4 hours time. And I'm not gonna, because it tastes like crap.