To answer the question most frankly, Russell, I think that this pain slut you speak of was playing a variation of a power game I've always called "I've Got A Secret" or "I Know Something You Don't" by renaming subspace something else so only she had been there, and only she knew the "real deal."
I say that for reasons pointed out in the thread already. "Subspace" by whatever name:
1. is not always reached by the same way for each person
2. it does not have the same "threshold" or edge of entry for each person
3. it is not equally "black and white" about whether one is "there" or not for each person
4. once reached, is not "A" place for every person, but rather, for some, is more and/or less intense while on the "other side," that is, being within subspace has degrees of intensity.
I say "pah" on her contention and drive rather to what she thought to gain from knowing more than you, the Dom to whom she spoke.