Rosa Hubermann and Max Vandenburg

Hans Hubermann has a very obvious reason for letting Max Vandenburg into the house, because of his promise to Erik.  What was a little shocking to me, and Liesel, was how Rosa accepted Max right away.  Since the title of this chapter is called "The Wrath of Rosa", and Rosa says, "Was ist los?" (what's the matter?), I imagined her screaming it.  Instead of glowing with rage at Hans for putting them all in danger,  "Her plum figure glowed with worry."  Then I had a very big question.  Rosa says,  "Jesus, Mary, and Joseph, another one?"  Had there been other people who he had promised anything, or is just a reference to Rosa and Hans bringing in foster children? Is Rosa just treating Max as another foster kid?