I spanked her sister for stealing the teacher's phone and they questions her about how I discipline the household
There's nothing at all wrong with that.
Schools can talk to their students without parent permission anytime. In this case, apparently, someone heard about you spanking the sister (I don't know how or where they would have heard that), and they questioned your daughter to try to understand what's going on. School administrators and teachers are mandated by law to report any suspected abuse or neglect that may be happening to any of their students. So somebody apparently asked your daughter some questions to find out what happened. An occasional spanking for discipline is generally acceptable. But if it crosses the line into beating, that's not.
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