I NEED HELP GUYS

My girlfriend and I have been dating for almost three years, we have a seven year old son (not biological) . My girlfriend wants a little girl so bad and it gets AGGRAVATING I feel like she pressuring me into something I know we both are not ready for. I've told her no,el no,hell no, baby language uhn uhn.... She thinks I'm being mean, I'm not listening to her, she even went to the extreme of not having sex with me. What can I do so she can better understand where I'm coming from?