In a previous thread, in order to say She doesn't know what she's talking about, you would translate it to
Elle ne sait pas de quoi elle parle.
But, I was thinking it could be
Elle ne sait pas ce dont elle parle.
However, I was told that that was not French. Would someone be able to clarify? I see in a French grammar site,
Je ne sait pas ce dont elle parle.
What is the difference?