Joan blinked, more taken aback at that moment than offended. If Howard knew anything about John, he must have also known that the chances John would ultimately side with anyone but Sherlock were extremely low. Joan could possibly see John chiding Sherlock for being rude...it's what Joan would do, after all. But Sherlock wasn't being particularly rude. So Howard came off to her as not only rude himself, but also incredibly short-sighted when it came to his relationship with John.

She didn't say anything, since she wasn't addressed, and answered his nod with a tilt of her head and a narrowing of her eyes that translated to a really?