If the family of this student would, upon leaning of her becoming Muslim, prevent her from being Muslim and force her to remain a kaafir, and handing her over to them would mean that she would be exposed to harassment and tribulation, then undoubtedly what the principal of the school has done is a serious evil deed and a great sin, because this action of his will result in harm for this Muslim girl. The Prophet (peace and blessings of Allaah be upon him) said: “The Muslim is the brother of his fellow Muslim; he does not wrong him or let him down. The one who meets the needs of his brother, Allaah will meet his needs. Whoever relieves a Muslim of distress, Allaah will relieve him of distress on the Day of Resurrection.  Whoever conceals a Muslim, Allaah will conceal him on the Day of Resurrection.” Narrated by al-Bukhaari (2310) and Muslim (2580). What is meant by “he does not let him down” is he does not expose him to doom or leave him with those who would harm him, rather he supports him and defends him. Fath al-Baari (5/97). 

And the Prophet (peace and blessings of Allaah be upon him) said: “There is no one who lets a Muslim down in a place where his honour will be transgressed and his sanctity violated but Allaah will let him down in a place where he would love to have His help, and there is no one who helps a Muslim in a place where his honour will be transgressed and his sanctity violated, but Allaah will support him in a place where he would love to have His help.” Narrated by Ahmad (16415) and Abu Dawood (4884); classed as hasan by al-Albaani in Saheeh al-Targheeb wa’l-Tarheeb (5690). 

If this principal was unable to help her and support her, then at least he could have left her alone without committing this grave evil. We ask Allaah to keep us safe and sound.  

But if in addition to that he told her not to become Muslim, that is major kufr that puts him beyond the pale of Islam. 

Ibn Hajar al-Haytami al-Shaafa’i (may Allaah have mercy on him) said in al-I’laam bi Qawaati’ al-Islam(p. 31): Another action that constitutes kufr is when a person approves of kufr even if that is implicitly, such as if a kaafir who wants to become Muslim asks him to help him say the words of Islam and he does not do so, or he says to him: Wait until I have finished my work or my khutbah – if he is a khateeb. It is as if he is telling him not to become Muslim, even if he does not appear to be wanting to become Muslim.  End quote. 

Al-Nawawi (may Allaah have mercy on him) said in Rawdat al-Taalibeen (10/65): Approval of kufr is kufr, to such an extent that if a kaafir who wants to become Muslim asks him to help him say the word of Tawheed and he does not do that, or he suggests to him that he should not become Muslim, or he suggests to a Muslim that he should apostatize, then he is a kaafir. End quote. 

What every Muslim who knows about this girl’s situation should do is try to stop her being wronged and enable her to embrace Islam and practise it, and tell the authorities about the harassment to which she may be subjected to turn her away from Islam. We ask Allaah to help her and make her steadfast in adhering to the truth, and to divert evil away from her as He wills, for He is Able to do that. 

And Allaah knows best.