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.
When Lena goes into bathtub, she has a piercing in her nose. Just a moment before she dives completely into the water, the piercing is gone.
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).
At one point, the siren of a police car can be heard. However, this is not the typical sound German police cars use.
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.
In at least two scenes the characters go within short time to places of Berlin which are situated several miles from the previous location.
The safety cars the girls drive after the police raid have completely tinted windows for obvious reasons. However, cars with tinted front windows as shown in the film are strictly forbidden in Germany, as such are highly suspicious, and would be stopped by the police immediately - making them useless as getaway cars.