Interference??

[Stair-Climber]

Coach argued with me for two days on this one. Girls 10 and under tournament. R1 on first base. Not sure how many outs--doesn't matter. B2 hits grounder to F4 (positioned in the base line between 1B and 2B). R1 stays on and around 1B (stands on 1B, comes off a few feet, goes back to 1B, comes off a few feet) and does not advance toward 2B. I am immediately thinking easy force out at 2B. F4 should have simply either went to 2B for force out or ran the ball to 1B for tag out of R1 and possible double play. Instead, F4 just stands there in the base line (between 1B and 2B), holds the ball too long and then makes a bad throw to F3. F3 misses the ball and ball goes into foul ball area and to the fence. R1 goes to 3B and BR goes to 2B. Play over. Coach of defence complains that interference should have been called on R1 because F4 could not throw to F3 at 1B because R1 stayed at and near 1B (and, in the coach's opinion, was in the way of throw). In other words, coach complained that F4 did not have the opportunity to throw to F3 because R1 was standing in the way. I told the coach that R1 had the right to be where she was at (in the base line at 1B) and was not to required to run to 2B. Additionally, I told the coach that his F4 had an easy opportunity to make force out at 2B or run the ball to 1B for tag out. Also, R1 did not intentionally interfer with throw to 1B--she simply stayed at or near 1B. I know that this is a kind of a HTBT but did I make the correct call according to how I explained it? Was R1 required to run toward 2B with F4 standing in base line with ball? Another question: If F4 did run the ball back to 1B and R1 and BR both standing on 1B. Which player has the right to the base?