It is responsible of you to be making a serious assessment of this situation and recognizing that a hard choice may have to be made. Entering into marriage requires huge commitment from both parties, and there should be clarity about what each of you are commiting to. Otherwise you risk ruining your lives.

You mentioned above that you were thinking about giving your girlfriend a choice. It may be that you are the one who has to make a choice. For you to tell her that she must "accept" your family is actually pretty vague. "Accept" could have different meanings to different people. A promise "to accept" is actually rather meaningless, IMHO.

I think your girlfriend has already made her choice and is living it. She wants you and is willing to be your wife, and she will have as little to do with your mother as she can arrange. It's a case of: "What you see is what you get." I don't think she will change. I don't think she can change, regardless of what she might feel pressured into promising. That puts the ball in your court.

I think your gf is moving forward in the hope that, little by little, you'll come around to her way of thinking, as to how the two of you will arrange your future. After all, you've stayed involved with her for 4 years. For all I know, her ideas about how to build a life together might be more realistic than your ideas. I'm in no position to know. Even in the most traditional corners of the world, things have been changing and will keep changing. Also, there is no part of the world where some mothers don't try to overly control their adult children. Those kind of mothers have been around everywhere, since the world began, and there will always be mothers like that, forever, in every culture. I don't know your mother or you. Your gf probably thinks that your mother wants too much control of your life. After 4 years, these two females have had plenty of time to size each other up . . . and they have done so. Each sees the other as a threat. In order to please one, you are going to have to disappoint the other. Neither wants to lose. Neither is going to give in. When you say, "I want you to accept my mother.", your gf is thinking, "You want me to let your mother run our lives." Maybe your gf is unfair and unreasonable. Maybe they both are. I don't know.

Your dream is for all of you to get along in peace and harmony. That's not going to happen. You have a choice between living with friction between these two ladies, or breaking up with your gf. But ask yourself: Is this gf being very difficult around your mother, or would your mother probably have trouble getting along with any girl you bring home? Just as an aside, how did your mother get along with her mother-in-law?