Another "Interference or Not"

[varefump]

Play: No outs. Batter takes called 3rd strike. Catcher doesn't catch the pitch and it goes to the backstop. Batter heads for 1st base and is running legally in
the 3-foot running lane. Catcher retrieves the ball from the first base side
of the backstop and throws to 1st, striking the on-deck batter in the back (or side), as she was watching the batter-runner and not the catcher. The on-deck batter was (a) in her own on-deck circle or (b) walking towards home plate to pick up the batter-runner's bat, when she got plucked. There was no intent to interfere but she also did not make an attempt to avoid the throw, seeing that she was not watching the catcher.

Questions: Is this interference on the on-deck batter? Is this one where 'intent' is required? If not interference, do we kill the ball to prevent further advancement of the BR?