Boston Police report a Jamaica Plain woman showed up at her ex-boyfriend's place in Roxbury last night, demanding he come down and fight her - or she'd return with a couple of friends to beat him up. And sure enough, she showed up with a couple of friends to help her beat him up, not counting on the fact he might have called 911 in the meantime, police say, adding they arrested her and, on booking her, found a loaded gun in her backpack.