I called my girlfriend "Fat" and now she's all Pissed!?

We were having an arguement and she started to call me very offensive names.....so I called her fat. That's right.....she called me all these names and I just called her...."fat" and she got all pissed like a madwoman. Now she doesn't want text me or talk to me and it's been almost 2 days. Is this my fault....granted, I know according to feminists a girl can call a guy 8 different names but a guy can't even call her 1 name....but should I really apologize or should I just let this thing go because obviously she isn't mature enough or manly enough to apologize herself.