I’m sure this is very frustrating. The question I ask of you is why do you keep fighting with her? A fight takes two people. The way to avoid the fights is to refuse her invitations to do it. Nothing you can say now is new information. What you can do at this point is remind her that you don’t want to fight, but you don’t want to give in all the time either. Just ask her to honor your feelings and do what you think is best.
If this constantly causes an uproar, you may need to rethink this relationship. Your girlfriend seems to think that love means that two people become “one”. They don’t. In a healthy relationship, each person retains their individuality while still doing their best to please the other. The individuality is what makes a relationship rich and what helps each person grow.
I suspect her insistence that you always agree is grounded in some insecurity. It may be that she is afraid that differences mean that you can’t be together. You may be able to give her the reassurance she needs. If not, only you can decide if her other qualities make it worth putting up with her demands for agreement.
I wish you well.