Dropped 3rd strike and BR interference

[Hoosier_Dave]

1st year ump and not all that familiar with rules yet.

1. Batter gets called strike 3; catcher drops ball. Batter proceeds to dugout not realizing that ball is dropped. I call batter out because she headed to dugout and did not proceed directly to 1B. Coach disagreed. He said that BR can go to 1B untill she is in dugout. I can't find the rule to support me or him. Can anyone help here? What do you do? We are talking about 14U instructional league. I understood that once girl starts toward dugout, she has committed to that and cannot go to 1B.

2. Batter hits fly ball 10 feet down 1B line heading foul. Pitcher is running to catch. BR and pitcher collide in foul territory. Interference? What is ruling?