Barbara already knew Booster's shield had been broken and managed to confirm how Ted gimmicked it into working again, appealing to Ted's vanity. Harley was not surprised when the shield became disabled (although she's kind of crazy and might have assumed stuff just happens for her). If you take the principle that one should take the most charitable reading of a scene in order to preserve characterization, it's probably fair to assume Barbara played Ted in order to end the fight. Not saying the rest of the text will back that up when we see the whole issue tomorrow, of course.