Scans_Daily

it's... complicated.
there is that, but there is also the part that Aslan is Jesus Christ and the kids being sent to the christian heaven while the text explicitly says Susan is not welcome there (at least right now)
There is also the part in which Susan may be a stand-in for Lewis himself and his own personal stuff and his own personal tragedies.

Then there is the discussion between authorial intent (what the author intended) and wether it takes priority over reader interpretation (ie, the text seems condemning of Susan)

On why the witch is here, the dream sequence is not necessarily supposed to be "the last battle" specifically (you will notice only the siblings are present), but rather using familiar iconography in a way that is disruptive of the original text.

Jadis is the most well known and familiar anatagonist of the Narnia books (even before Tilda Swinton's wonderful performance) and more likely to be familiar to most readers than... say... Tash, Aslan fundamental opposite with the head of a bird and who you can easily confuse with smoke....