I completely understand where you're coming from. On my DH's side of the family, out of 3 generations there are only 2 women and 9 men/children. So of course my MIL has put all this pressure on me to have a girl this time around. She recently told me that she would be "disappointed" if my baby wasn't a girl. What kind of grandparent says that? So after she made that comment, I decided that I didn't want her to come to the gender u/s. Of course she acted like she was all upset. Whatever. I'm extremely tempted to not even tell her the gender when we find out on Monday. lol I can only imagine what she would say to that. I know that if we did have a daughter, that she would favor her over my sons and I can't have that. I don't want my beautiful little boys to think that their grammy loves their sister more than them. But anyway, I definitely feel the same way as you. Even tho she gets under my skin, I'm scared of disappointing her (as stupid as that sounds). What's crazy is that they never realize that how they're acting is wrong and offensive. And I know that no matter what I say to her, she'll never change. Oh well. Just wanted you to know that you're definitely not alone.
I forgot to add that I always hear that "Sean (DH) doesn't make boys" comments from my mom and sister.. so I have it coming from both sides of my family. Sigh.