User blog comment:HandsomeBanana/Brandish magic theory/@comment-26287497-20150710150306/@comment-7418318-20150713081209

I think it was the other way around. Lucy and Erza were taken by surprise, while Brandish already knew her subordinate's magic and thus was prepared.

Either that or she's just too freaking strong for him to take control of her magic.... yep that's probably it.