I had this exact same play at a camp several years ago. Player dove for aloose ball, slid to a stop right next to the sideline but her ponytail kept goin a good one inch OOB. I had one clinician tell me that they would have let it go, and another say it was a good call. Lead to a big argument among our clincians. (I think this was before the rule was established/clarified)
I did offer a solution. I had said if the player had a weave, then she would have NOT been OOB b/c it was not "really" her hair, it was someone else!!