The character from the 2013 short film played by Lotta Losten is Esther from this film. The short film shows what happens when she makes it home from work.
Though likely not, as she wouldn't have done the idle wondering that she'd initially done while flicking the light on and off.
While the Focus Group Ending altered things so that Sophie's suicide wasn't a Senseless Sacrifice, the evidence in the basement indicates that Diana never actually goes away without that link - she just can't interact without it. And given that Rebecca watched her own mother commit suicide, and that Martin lived in the house for his entire life while Diana was there, who's to say she didn't establish a link with one of them?
Given there's a sequel on the works, it seems that Diana is indeed still out there.
