I always assumed and am still assuming that the purposes are three things:
1) Her crew finally arriving and making things tenfold worse for the mcs
2) Defeating two Yonko at once
3) Her interest in the Poneglyph complicating things
1) Her crew finally arriving and making things tenfold worse for the mcs
2) Defeating two Yonko at once
3) Her interest in the Poneglyph complicating things
The Wano plot around her is part of the worst things of the arc