HTBT, but also, with the way the play sounds, you could probably have been slightly more lenient with the runner, as she technically has 3' to run to the outside/inside of her base path not just a 3 foot-wide running area to step in.
And I agree with above, as 8.7.A. states "..to avoid being tagged by the ball in the hand(s) of the fielder." - No ball in the hand(s) of a fielder attempting to tag = no running out of the base path.