She killed them because they were loyal to Marko only (I wrote Mergo because of Bloodborne ahah). Hence, during the film there is a scene where there is a sort of vote, and the majority vote for Marko, making Mother Suspiriorum lose. In brief, Suspiriorum killed those who were not loyal to her, but to Marko.
Basically, it's contemporary with references to expressionism and hints of Indonesian.
From the choreography Wikipedia page for Susperia (2018):
Guadagnino's Suspiria utilizes dance as a key plot device. Congruous to the period in which it is set, contemporary dance was a central influence on the dance style depicted in the film. Kajganich commented that ...