My quick comments due to time constraints:
Size doesn’t matter. Your being silly. I actually thought the “too big a dick” to fit or suck quite funny. Maybe she remembers it as a silly episode during her rampaging years. I have a friend who says he is huge… and he doesn’t like it being so. My GFs have always said my size is perfect. Big enough to please… suck and to get some anal sex without killing someone.
I think your SO is a bit callous in making her comment. Does she say silly stuff at the wrong time ? (Like being honest about someone looking awful for example) If she does it with other topics… chances are she did the same thing talking about sex in the past.
I think your an insecure git (just like I am) and you should just go ahead and give her some hot sweaty sex and get over it. Big dicks aren’t a good thing. They do make funny stories.