From what I understand it Emma transferred it from her mind to Scott's mind. Thus, why she is no longer in her diamond form and Scott is using techniques that Jean taught him to seal off that section of his mind. And remember he got so well at doing that, there was information in there that not even Emma could get too if she tried.
All this, is pretty much just a filler issue. And I don't think Catwoman is really that much of a babysitter. Just didn't want to put up with any crap Harley might cause if she went out by herself.
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