I can see why it would be tempting to think that ‘Babylon the Great’ is Jerusalem based on the ‘get out of her’ as an analogy for Jerusalem’s destruction, but that is incorrect.
Though earlier writing of the ‘gospels’ is traditionally proposed to make parts seem prophetic, there is no tradition of an earlier writing of Revelation. The destruction of Jerusalem, including references to the period from 66-70, is already described in Revelation chapter 11. The destruction of ‘Babylon the Great’ refers to a later (hypothetical) destruction of Rome.
Revelation 17:9 identifies ‘Babylon the Great’ as sitting on 7 hills, easily recognised as ‘the seven hills of Rome’. Revelation 17:18 also says ‘Babylon the Great’ is a city with a kingdom over other kings, which very accurately describes the relationship between Rome and its various client kingdoms (one of which was Judea). Those descriptions do not fit Jerusalem.
Hence, ‘get out of her’ is better seen as a warning to Christians to avoid Rome. This would be particularly relevant during Trajan’s reign when Revelation was likely written.