Quantus, I read that same quote and I came away with that the ward came up in response to what Lily was doing, not that she called it up. It was the part where Fix said "But"...
Hmm. I guess I can see how you could read it that way, but it makes less sense that way to me, if the goal was to try to trick/convince Alfred to activate something they'd have both gone straight to doing that. The fact that they instead had Maeve try to
Distract Alfred while lily went and did something else implies that they were specifically trying to do something without his notice, rather than the opposite tactic you describe.
Also, as more general support of the stance, Alfred has made repeated references to how it is the Warden's job to make those choices and activate those sorts of defenses, not "Here's"