Obstruction or not?

[IamMatt]

14U batter hits grounder to F5. Right-handed F3 has her foot planted on the white portion of 1B and her glove out waiting for the throw. F5's throw is off a few degrees to her right (or clockwise) so that rather than going straight to F3's glove, the ball will intersect the baseline a foot or two towards home plate.

This causes F3 to turn or pivot and reach across the lane in front of the orange portion of 1B to make the catch just as BR is arriving at the base, so that F3 is blocking both sides of the base before receiving the ball and her momentum is also causing her to step with her not-planted foot across the baseline, leaving a footprint about a half-foot into foul territory and about a foot in front of 1B.

In order to avoid a collision, BR puts the brakes on, which slows her enough so that the ball gets to F3 before BR hits 1B.

Out at first? Obstruction? Any questions need to be answered to make the call?

What it BR had not slowed down and had collided with F3 just before the catch?

Thanks.