Kevin Garnett's younger sister is in serious trouble after cops say she tried to rob THREE check cashing stores in South Carolina ... while making bomb threats.
It all started on Monday ... cops say Ashley Danyelle Phelps tried to rob a Check Into Cash in Greenville -- and told employees she had a bomb. Someone pressed a panic button and Phelps fled without any loot.
The next day, cops say Phelps tried to hit another Check Into Cash store -- but failed -- so she went to an Advance America shop instead and once again told employees she had a bomb.