Sorry for the necro-post.
I believe she murdered them, and I think she even 'sent back' the REAL Pinkie Pie. As when we first saw Pinkie go through the pond, she WENT THROUGH the pond, she didn't just recite the spell.
And I think she went into another universe, or the Pinkie Pie we saw first was in the other universe. The lack of knowledge of friends and decent into madness from the 'copies' could simply be because going through the pool does that to ponies. The ponies are clearly sentient, as they form sentences during the paint scene, and obviously can speak and retain information. Maybe the dumbing effect wears of after a few hours, just in time for the paint experiment.
And I also think she killed the real Pinkie, as there was clearly one Pinkie out of the two Pinkies left that was nervous about the experiment and clearly wanted to win. Or if that wasn't the real Pinkie maybe the real one was killed by being distracted by another pony, because clearly being distracted equates to not being real.
The whole thing about them being made out of magic is just nonsense, as magic is not the explanation for EVERYHTING!