Because she is your gf, I think it should be handled in a mature way instead of quarrelling and debating over which religion is right.
But I like to ask a few questions to test your faith in your own religion to see if you really have faith in what you believe in, or you just follow your parents religion blindly.
1. Why does dead people need to eat on joss stick?
2. Your ancestor depend on you to feed him with joss stick daily, what if you forgot to feed him, double die?
3. The joss stick just burn and the smoke go difuse out, if there are nearby ghost, can he eat too?
4. Sometimes I see people offer real food, so does your ancestor eat food or joss stick?
5. Paper money = their currency?
6. If you have no family, no one burns money for you, you will be beggar after dead?
7. Can you burn money for yourself first, then when you die, you got more to spend?
8. Why does hell open the gate (Gui men) for 1 month every year? (If Changi prison do that, I think chaotic sia.. somemore we are talking about mortal and nether world here.)
9. Who is the strongest god you think?
10. I heard from stories and show that alot of gods are once mortal, so we can train and become god?
11. So who created earth? (big-bang theory? evolution? creation?)
If you are able to answer some of these questions with reliable resources, then it prove that you are not having a blind faith like your gf. Else, maybe you should try listening to what your gf says? Instead of block her out.
But I do have something against CHC. That will be another story.
U can also ask your girlfriend to see if she really understand her religion or not
1) Why do people have to keep praying and praying to god ? Do god really desire u to waste so much time ?
2) Does god send u to heaven and hell simply on how u praise him ? Isn't tat the easiest way to please egoistic people ?
3) Why r there so many different denominations for christians ? Which is right which is wrong ? Wat happened to the holy spirit or supposed clearly defined bible ?
4) Why r there so many flip flop in christian policies ? (inquisition, crusader, slavery, evolution to a certain extent, OT and NT)
5) They say tat god forgive all sins if u r truly repentent. Doesn't tat means the best time to believe and be repentent is just before u die ?
6) To many christians, deeds is not important, just faith. Doesn't tat encourage people to be fanatic instead of doing good deeds ?
7) Why do u believe the bible is true ? Just because the bible say it is true ?
Why do jesus have to die in order for god to forgive and not simply god just forgive ? It is like in order to forgive the person who insult my religion, I kill my son. It doesn't make sense
9) Why r there so many contradictions in the bible ? A classic example is the events on the day of jesus resurrection. Different books give different accounts
10) Creationism has no evidence to back it up and it is no different from tales like pang gu or other mythical folklore. Why believe in them and not evolution which have many undisputed evidence ?
I don't think it is fair to consider christainity as a religion tat is fool proof and not have its share of criticism. To many people, believe is a choice. However to my understanding, wat u believe is based on wat u preceive as truth, and cannot be forced or choose. If u do not believe in her religion, then state it as such and ask her to understand. If she cannot tolerate a non christian boyfriend, then the choice is not really yours and u can either convince her to change her mind or break up. Changing a religion because of girlfriend and not because it make sense is an extremely foolish thing to do.