Runner caused fielder to change direction??

[WAZebra]

Situation: Runner on 2nd base. Ball is hit to SS. Runner slows down to let ss pass infront but then the ss steps back one step, runner then continues to 3rd base. No contact occured. Ruling by the umpire at home and confirmed by the field umpire is that the runner caused the fielder to change direction, therefore she is out for interference.

Please tell me your thoughts about this situation.