My girlfriend told me about this film so i may not be 100?curate on what happens in the film, apologies.
In the film, a woman has an accident and whennshe returns home, she finds her family are all acting off, something seems wrong about all of them.
Somehow she learns that they were replaced by their mirror selves, who killed them and wanted to live their lives. She kills her mirror family and she and her dad barricade up all mirrors to stop her versioj coming through. One day she spots blood coming through the ceiling and goes to investigate only to find its her body. Turns out she was the mirror version and had killed the real version of her but forgot thanks to the accident.
At the end of the film, her dad comes to check on her and sees her from the window smiling creepily and he immediately knows she’s the mirror version and runs.