Yeah she used take over to gain control over Seira's Macro magic, however that doesn't instantly mean it's permanently as Take Over is supposed to Take Over souls. The fact that she issued the command of Elfman attacking Seira, who was under the control of Seira, it's possible she took her Macro magic over for a brief moment and in that moment issued the command via Seira.
Unless Seira lost her magic, in the case Mira than really would also have Macro magic, it means she duplicated it, but how was she then able to command Elfman? Who was under Seira's control?
So I find it very plausible that it was a temporary take over just to issue that command.
Well yeah it's not like that Natsu ate up the entire Etherion tower or ate up all of Laxus' lightning or that Gajeel ate up hundreds of shadows.