How is obstruction called on the catcher on a play like this? If the ball is coming in to her or if she has the ball before the runner gets there, she has every right to block the plate.
As Scott and Tom have suggested, if the ball is "coming in to" the catcher and she hinders the runner's progress, that's obstruction (in ASA at least). They took the "about to receive" exception out of the rule some years ago; you have to actually have the ball.