#13: it seems a little strange to me to assume that the present perfect is necessary without more context....
-- absent, of course, some particular instruction like 'Use the present perfect.'
That's precisely what there is here, of course: 'make present perfect questions'.(OP)
So obviously it's artificial and there is no context. But the speaker could mean, for instance,
'What has / What's she told them? (i.e. what information are they in possession of?) -- I need to make sure my story tallies with hers.'
That doesn't presuppose that she's still with the police. She may have spoken to them more than once, anyway.
#9 I can't think of a scenario where I would say "What's happened" or even "What has happened" instead of "What happened".
As KinkyAfro has implied (and most readers of this thread will know), in BE there are times when only the present perfect is idiomatic.
For 'What's happened?', the 'loud noise' example is perhaps not the most clear-cut.
But recently, for instance, someone said to me, 'I'm sorry I haven't phoned you for a while, but I've been really upset.' My immediate response was, 'Why? What's happened?'
Or if someone suddenly rushed in, deathly pale and distraught, you would probably ask 'What's the matter? What's happened?'