My girlfriend is in a different church from that of mine ,she has refused to join me and am ready to join her church .what can I do???
What exactly is the issue? From what you are saying it seems like you have agreed to join her church. If this decision makes you uncomfortable, then talk to her more and both of you agree on what and how you want your relationship to move on. Even as you plan to talk to her and despite the different churches, you need to ask yourself if you share the same values, goals, interests, if so then you both should be able to address the issue of the church.
Check out this article: https://lovematters.co.ke/news/religion-it-big-deal
Wish you the best.