PS -- absolutely the correct call. The only thing I would add is that U1 should have killed the play, not called the out. I am assuming he did not know about the obstruction call though. The PU who made the call was turned to where U1 couldn't see the arm. I would advise PU to make that call bigger and louder, and turn to the plate so U1 has a better chance of knowing it.
This is all just a thought exercise because the run scoring ends the game, but what if this wasn't a game-ending play? If U1 kills the play after calling her out -- I assume proper mechanic is to call the out, then kill the play, then defer to PU for the runner placement since that's who called obstruction -- what would you do with the batter-runner? She was on her way to second, so do you award her second? Make her go back to first? Is there a rule or umpire judgment?
Also, moot point, but the batter-runner was very obviously obstructed, too, and that was missed. Probably a good thing they got the first one right.