OP didn't really say what the pitcher did instead of throwing the ball to 1B. Presumably she either made a play on the runner on 3B or simply checked her, which would be scored FC.
ATEC Fielder's Choice:
3. when a ball is put in play where a play is made on any lead runner and an out occurs, or an out would have occurred had no error taken place, or the runner is safe, but the batter would have been out had the initial play been made at first,
4. when a runner is checked and no throw is made ...,
NCAA Fielder's Choice:
14.7.1.4 When a runner is checked and no throw or a late throw is made, but the runner would have been out had the initial play gone to first base.
Note: Defensive indifference is scored as FC.