I guess since I don't know how things actually happened when Holly was taken so I can't really say too much, but I wonder why they never gave McGonagall a communication device knowing that they would need her and time was of the essence.
As a matter of timing, it wouldn't have mattered. Holly was lured into the ambush Sunday afternoon while McG was still out greeting new muggleborn students. Originally I wrote it as Hermione making four coins with one for McG, but explaining it would have taken more time at both ends- how she got it and why she couldn't respond immediately. I doubt any of them expected Pansy to be activating it so soon.
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