How do you come back from that when she doesn't take you serious?
Actually, the good news is that the less you've done of that (standing up for yourself) in the past, the EASIER it is to make a pretty bold statement. She expects so little from you, that it wouldn't really take much to represent a "180" for you.
Do NOT operate from a position of ANGER or RAGE, however. Real men command respect by calm, steady strength, not by angry outbursts.
I suggest you do a Search on Robx's posts, and take a few days to read them. Your answers lie in their wealth.