Grammar of "Use to Be" or "Used to Be"



Hello! And thank you for your question.
The main difference, is that 'used to be' indicates that it was a condition in the past, but it is no longer like that. I would infer from that sentence that her old school is no longer so strict. However, if you said, 'My old school is so strict', it would indicate a condition that is ongoing - nothing has changed.
I hope that this helps you. Please feel free to reach out with more questions.