My girlfriend believes that she is Jewish, but actually only her father was Jewish. She did not commit yet to undergo conversion. Meanwhile, I try to convince her that she needs to go to mikvah every month, but my friend told me that there is no point in her going to mikvah until she is fully Jewish. Please advise. Thank you.

 From an Orthodox perspective she is not Jewish

WE also dont condone premarital sex

and going to Mikvah is not relevant to someone in her position

or in yours

1. Your girlfriend’s Jewish identity.   You state that she believes that she is Jewish, but that she is in fact not halachically Jewish – by which I think you mean that you don’t believe that she is Jewish (or, in your friend’s words, “fully Jewish”). Does that matter to you? Clearly, it seems to matter – yet it hasn’t prevented you from befriending her. Is there a contradiction here? How is it that you have been willing to become the boyfriend of someone who is not Jewish – if her Jewish identity matters so much to you?  And if it doesn't matter that much, why are you making an issue of it?
2. You state that your girlfriend hasn’t yet committed to undergo conversion, which means that she may indefinitely remain a patrilineal Jew. Yet you seem to want her to go to the mikveh each month. Is that because you are having sexual relations – even though you are not married? Under what theory is that consistent with your concerns about your girlfriend’s Jewish identity?
3. What is the role of Judaism in your life, and what is the role of Judaism in the life of your girlfriend? Have you talked about that? (Hint: you should!)

This is an interesting question and actually points out a situation that would have been unheard of 50 years ago.  People claiming they are Jewish and wanting to be recognized as Jews.  In decades past, people were either Jewish or not and, if they were not and wanted to become Jewish, they would convert. 

 

However, today people can claim Jewish status by dint of the fact that they are born of a Jewish father even if they have absolutely no connection to Judaism.  The Reform movement created this situation when it accepted patrilineal descent.  But a lot of people misunderstand what this means.  It does not mean that, just because someone has a Jewish father that they can claim they are Jewish.  It means being raised as a Jew, educated as a Jew and, if they are an adult, embracing Judaism only. 

 

However, I personally, have some issues with even this, even though I agree with the idea of patrilineal descent.  It seems to me that someone who has a Jewish father and wishes to embrace Judaism later in life should make the commitment publicly by the process of conversion.  This is where I think your future wife should be.  There should be a process of study and conversion which implies commitment to the Jewish people.

 

Going to the mikveh every month is the least of the issues.  Actually, I think that without a public commitment to the Jewish people and a sincere desire to become a part of the Jewish people, the mikveh is the least of the challenges. 

 

Patrilineal descent is a wonderful notion except when it is used as a 'cop-in' - a way to get around conversion.  If your soon to be fiancee is serious about Judaism, she ought to be serious about what Judaism requires in the form of commitment from someone who has never been educated, raised or practiced as a Jew before this moment.