[TronDD]

The way I see it (it's been a while so forgive me):

Spoiler:

Rumi (the fat chick agent, right?) was insane. She was doing the killing and pretending to be Mima (main character?). Rumi was driven to do these things sort of to protect Mima who she believed (or wanted to beliove) was herself, I guess. Mima, who was having a stressful time adapting to the acting lifestyle after abandoning singing, thinks she is going nuts. That's why she sees herself all over the place.

Seeing the alternate Mima doing things was the director's (writers?) way of bringing the viewer into the paranoia and psychosis that Mima was imagining.

So Rumi was doing it, but Mima, and the viewer thought Mima was doing it.

Clear as mud?