In the DC animated movie Injustice a superhero catches the Mirror Master from the mirror world. Who is this character, and how is she able to enter the mirror world i.e. which of her powers helps her in entering the mirror world?
That's definitely Raven (Rachel Roth).
From the Injustice: Gods Among Us Wiki:
Raven is the half-demon child of the demonic overlord, Trigon, and as such is one of the more powerful magical users seen in Injustice. Raven can manipulate dark streams of magic for various uses, such as conjuring barriers to absorb or reflect projectile attacks sent at her, shoot blasts of dark magic at her enemy, and use telekinesis to contort and control her opponent's body to her whim. As an empath, Raven can also sense and absorb her opponent's emotions to draw further strength for herself while weakening them, or even gain total control over their body and mind, controlling their actions and even speaking through them.
In the comics, Raven is a character mostly associated with the Teen Titans.