That's a good point. Actually, don't we have some vignettes of Trelawney under prophetic pressure after that incident? That would explain the lack of any Hall action, if the prophecy is not yet done.

Still leaves Dumbledore a mystery: if Trelawney stopped after teleporting away, and this proves it wasn't about Dumbledore, then what is stopping him from sitting in Trelawney's office and one by one summoning suspects until she suddenly bursts out the rest?