User blog comment:Zathronas/Speculative Author - RWBY Relativity/@comment-25396609-20160225025456/@comment-26397825-20160225035841

From the transcript in The Emerald Fores:

Pyrrha (off-screen): Aura is the manifestation of our soul.

This means that in aura to generate aura, she has to have a soul. While it is true that they have learnt how to transfer souls, the implications from Penny's quote is that she generates her own soul, and therefore aura, which in turn implies that her soul is a new one and not something taken from someone else.

Both ways are viable, but so far my understanding of the situation is that Penny was an artificially created soul for the express purpose of finding out if they could do it.