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.