When Lena calls the policeman she dials a mobile number (prefix 0174). Right after she finishes dialing you can hear the ring tone. However, when you call a German mobile phone there is a distinctive pause (ca. 6 seconds) between typing the number and hearing the ring tone (the connection to the mobile phone is established in this time).
Charlotte intends to kill herself by exposing to sunlight. She locks Louise and Lena inside so they don't stop her. Louise bangs the door so hard we see it bending from the outside. But when we see her again banging the door from inside, it is intact.
In the montage sequence in the beginning Louise's face is (inexpertly) photoshopped into Menzel's Flute Concert of Frederick the Great. Actually, the person sitting in this position in the painting is Frederick's sister Wilhelmine.
The safety cars the girls drive after the police raid have completely tinted windows for obvious reasons. But cars with tinted front windows as shown in the film are forbidden in Germany. However, this is probably intentional as Louise is wealthy and might have gotten the cars through illegal ways as an emergency escape plan.