Well she doesn't have to actively think about the illusion to keep it going - she just needs to actively think about it to summon it.
My interp (which you can correct if wrong) is this: She doesn't need to think about an illusion to passively maintain it. So, for instance, if she made an illusion of a barbed-wire fence across the field, she could set it and it'd stay there without any further input. But she would need to exert conscious control to make an illusion move. After all, the illusions aren't sentient or autonomous; they do what she tells them to. So she'd have to actively script each motion, e.g., now the illusion of her is fleeing; now it's leaping over the enemy's head; now, since it's been "hit," it's staggering backwards with a bleeding leg.
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another place and time, without a great divide, and we could be flying deadly high