She wants some advice for her Christian classmates

Firstly: 

We appreciate your protective jealousy (gheerah) concerning the religion of Allaah, may He be exalted, and for your interest in calling others to Allaah, and we ask Allaah to guide us and you and to make us and you steadfast. 

Secondly: 

We do not advise you to debate with your Christian colleagues, because you stated that they have specious arguments that you are not able to refute, and you said that you are a beginner in seeking knowledge. This makes us repeat this advice in your case and the case of those who are like you.  The principle is that the permissibility of that is limited to situations in which the interests served by doing it are greater than the negative results thereof, or in situations where arguing is kept at a level of friendly debate rather than fighting.  Fath al-Qadeer by al-Shawkaani, 1/527. 

The purpose which you seek to achieve by debating with the People of the Book or other types of people who associate others with Allaah, or people who follow whims and desires or innovations, can only be achieved if it is undertaken by those who are qualified for it, who have sufficient knowledge of their own religion and the other religion to debate it, and who also follow the shar’i etiquette that is prescribed for us in such matters. 

Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) said: 

Because the followers of the Prophets are people of knowledge and justice, when the followers of Islam and the Sunnah speak with the kuffaar and followers of bid’ah, they speak with knowledge and justice, not with speculation and whims. Hence the Prophet (peace and blessings of Allaah be upon him) said: “Judges are of three types, two of whom will be in the Fire and one in Paradise. A man who knows the truth and judges accordingly will be in Paradise. A man who knows the truth and judges otherwise will be in the Fire. And a man who judges among people on the basis of ignorance, will be in the Fire.” Narrated by Abu Dawood and others [and classed as saheeh by al-Albaani in Saheeh al-Jaami’]. If he is one of those who pass judgment among people concerning their wealth, lives and honour, and he is neither knowledgeable nor just, then he will be in Hell, so how about one who judges concerning sects and religions, and the basic principles of faith, knowledge of the divine and other fundamental pricnples, with no knowledge or justice, like the followers of innovation and whims and desires. 

Al-Jawaab al-Saheeh li man baddala Deen al-maseeh, 1/107-108. 

Because of what Shaykh al-Islam mentioned here about the etiquette of debate, Allaah says (interpretation of the meaning): 

“And argue not with the people of the Scripture (Jews and Christians), unless it be in (a way) that is better (with good words and in good manner, inviting them to Islamic Monotheism with His Verses), except with such of them as do wrong; and say (to them): ‘We believe in that which has been revealed to us and revealed to you; our Ilaah (God) and your Ilaah (God) is One (i.e. Allaah), and to Him we have submitted (as Muslims)’”

[al-‘Ankaboot 29:46]

Shaykh Ibn Sa’di (may Allaah have mercy on him) said in his Tafseer: Here Allaah is forbidding arguing with the People of the Book, if it is done with no knowledge of argument or with no appropriate basis, and He says that we should not argue with them except in a way that is better, with a good attitude, kindness and gentle speech, calling to the truth and making it attractive, and refuting falsehood and making it unattractive, in the most effective manner. The purpose behind it should not simply be to debate and argue, and loving to win, rather the purpose should be to demonstrate the truth and guide people. End quote. Tafseer al-Sa’di 743. 

You should also focus on seeking knowledge. Before a Muslim learns about what others believe, he has to learn his own religion and its rulings. So look for sisters who are seekers of knowledge and start to learn your religion with them. You can also make use of tapes by the scholars of Ahl al-Sunnah who promote the way of the righteous salaf, especially if there is no one available who can teach you. 

Your primary concern should be to learn that which will correct your belief and worship. Study the meanings of the Book of Allaah and the Sunnah of His Prophet (peace and blessings of Allaah be upon him). 

This is the sound way with which you should begin. Forget about debating with Christians and other followers of misguidance and leave that to those who are specialized in that field, for they are more able to debate with them and point out where they have gone wrong. There are still people in the Muslim ummah who can do this duty – praise be to Allaah. 

If you think that the Christian proselytizing is having some impact on your Muslim sisters, then you must warn them against making friends with these kaafir women or listening to them. You can also provide them with books and tapes which explain true Islam, and warn against false sects and religions. 

We ask Allaah to help you to do that which pleases Him, and to enable you to gain beneficial knowledge and do righteous deeds. 

And Allaah knows best.