Dual citizen (DE/BR), living in Brazil, wants a German account for modeling assignments - secondary residence with relatives = tax trap?

I'm writing this on behalf of my cousin. Initial situation: My cousin was born in Brazil, mother Brazilian, father German - dual citizenship DE/BR. The center of life, residence and job are entirely in Brazil. In Germany she is staying with relatives and therefore does not have her own apartment here. She now wants to open a German account - partly because she has been offered her first paid modeling jobs from agencies. Initial research suggests: that's what you need