My recollection of "Griffon the Brush Off" had RD being very angry at the revelation Gilda was a great big meanie-pants. RD's big thing is loyalty. That Gilda would mistreat her friends behind her back was seriously uncool. There's also something else to consider--this happens a day after "Canterlot Wedding". Dash may be keyed up because she's on patrol in case any stray changelings might be around.