I am so sorry that you had to experience this.
Honestly, if it were me, I would tell my mom to please not say things like that to me. I would try to put it in a polite way but make it very clear that she has really hurt your feelings. If she's anything like my mom, she'll probably throw a fit for a couple of hours but then come to her senses. I would also try explaining why I was wearing it that way, and that it will eventually look nice if it's given time to recover from the damage of straightening, but that straightening more will just make it worse in the long run.
But that's just my opinion, and it might not work in your case.
Good luck. I hope things start looking up.
HG products: AG Recoil, DevaCurl Set It Free