TEXARKANA, Texas — A Flowery Branch native accused of sending ricin-laced letters to President Barack Obama and New York Mayor Michael Bloomberg is competent to stand trial, a federal judge said Wednesday. During a brief hearing in Texarkana, Texas, Shannon Guess Richardson, who had moved to New Boston, Texas, from Jackson County a couple of years ago, also pleaded not guilty to two counts of mailing a threatening communication and one count of making a threat against the president of the United States. Richardson, an actress, is accused of sending the threatening letters in May to Obama, Bloomberg and a third man who heads Bloomberg’s gun-control group in an attempt to frame her now-estranged husband.