Change of status can be challenging. Previously US law permitted persons entering on tourist B-2 visas to change status to F-1 visas. That is no longer the case. You should apply from your country of origin or residence, and reenter US in F-1 status.
她5月剛籤的旅行簽證，8月換簽F-1，會不會拒簽？ 8月初遞交表格，能預約到8月份的面籤時間嗎？
No. Hard to say. There are a lot of students going abroad to the US to study. I suggest you give yourself more time.
像她這種12歲的小留，面試會問哪些問題？請不吝賜教，叩謝！
Some of the questions here are applicable. But not all since the student is only in middle school.
http://www.internationalstudent.com/immigration/f1-student-visa/f1-visa-interview-questions/
美國
加拿大
英國/瑞士
FindingSchool美高排名
