khaas,
If in the judgement of the umpire that made the call, the
runners action hinders, or confused the defensive players
attempt at fielding the ball, then this was the correct
call. There does not have to be contact for intereference.
Interference can be physical, visiual or verbal. You did
state she [R] did intentionally slow her pace. Sounds like
an act to confuse, or hinder to me.
JMO.
glen