IrishEMT has the correct answer: Maria Schrader (aka "Hannah") is German, and speaks English with a German accent.
As for bilingual children, they adopt the accent of the community in which they live, in particular, the accents of the other children in that community. In large foreign-language communities, for example, where one hears only Spanish on the streets, in the stores, on the playgrounds, etc., the children of these communities grow up speaking English with a Spanish accent.
However, there are no similar all-German communities in New York. Thus, Hannah should've spoken English with an American accent. This has indeed been my experience with native speakers of German who have grown up in the States: they speak without an accent in either German or English.
Not always. Besides, what you call a German accent is what can happen if the child "blends" the local vernacular --think NY--with that of the Parent. My Dad was second generation German and I a grew up in East Texas. I do not sound much like the average East Texan, except when I choose.