It seems like this Ghostface is trying to kill the last Woodsboro survivors (though Sidney's absence might make that a bit difficult) for an unknown reason (though, in true fashion, it'll likely relate to horror movie tropes).

Source: https://gamerant.com/scream-6-super-bowl-trailer-ghostface/

She has left Woodsboro but is brought back after her sister is attacked by the latest incarnation of Ghostface.

Source: https://collider.com/scream-5-why-that-cameo-doesnt-work/

Unfortunately, they won’t be able to escape a new Ghostface killer and a new wave of murders, but they will count on the help of two legacy characters: Gale Weathers and Kirby Reed (Hayden Panettiere), the latter a survivor of the 2011 Woodsboro murders.

Source: https://screenrant.com/is-gale-weathers-going-to-die-in-scream-6/