Thanks for the responses.
When the play happened, I knew that I wasn't 100% on the call, but I was working with a partner who is a very nice guy, but anything beyond safe/out, ball/strike, is out of his league.
The Batter moved out of the batters box as the catcher bobbled the ball, When the catcher picked up the ball to throw, the batter stepped back. I think she was trying to move out of the way, but she stepped right into the throw. I don't think she did it on purpose, nor do I think she really knew where to go or what to do. Since she was out of the box and took a step back as the catcher tried to throw, I knew I had Interference. I just had the penatly wrong.
At least the mistake was early in the season, now I can be that perfect umpire that the coaches and parents expect.
