I may be misunderstanding this, but she's not a Lolicon
meaning she has a young girl complex. She's a genuine villainess - as, apparently, are all successful witches - who's being defrosted by a sweet younger witch. The whole witch system seems pretty bad, anyway. Younger girls are just easier to use and abandon, is all.
Perhaps she enjoys using younger girls. Don’t kink shame her! ;) One could argue that—if she’s a “genuine villainess”—she enjoys being an opportunist. (Whether this has always been who she is, or what she became over time, it isn’t quite clear.)
What makes this a compelling trope is that—despite Melissa’s cold, uncaring disposition—she’s truly a tsundere when it comes to Tanya. She still seems to enjoy the naive nature of Tanya, but something about her has captivated Melissa in a way she didn’t expect.
I’m such a sucker for types like Melissa. God, I need therapy.