Diving into first on foul

Question
Hi.  I was just at a state championship game and our girl hit a foul ball down the first base line and the first baseman caught it.  We had a runner on first base when it was hit and she took off but only a few feet (on the grass) until she realized that it was a foul and she needed to get back. So she dove into first base and was safe.  All the umpires and coaches got together and decided that she was out.. why is that?  

Answer
Hi Lacey,

With the play coming from foul territory it's possible the 1st base umpire was blocked out on the play and the defense asked him if he needed help from his partner and the umpire agreed to check with his partner.

If his partner had a better view and she was actually out rather than safe they can change the call.

Other than that I haven't a clue as to why she would be out.

Mark