Maybe you know this already but platinum score is best achieved by "speedrunning" the encounter, not by killing everything possible (that is usually a byproduct anyways). You need to complete the encounter before the time on the left side of your screen runs out, "speedrunning" gives the most score. Not being able to kill her in that given time locks you out of platinum score. So the atraks nuke strat is the way to go, worked for my team at least. Edit: seems like its bugged for some teams, not all of them. Just destiny things.