Here's my take on what she is doing. She isn't like separating her soul/astral body from her material body, I think that's just a representation. What she is actually doing is probably something forcefully shutting down her thought process and/or active processes. basically forcing herself to go comatose
Man, if this story actually goes through with the torture. Then good on it. So many stories back out of anything like this real quick. Most of the time the torture will be quite mundane and not even all that scary looking. Would be nice to see a story go all the way with it.