Dont you hate this? weight on kids?

ok my niece is 11 and over 160 pounds. the last time she was on a scale she was 10 and 180 pounds.anyway her mom blames her weight on hereditary and i hate that. hereditary is not to blame the main reason is because hse lets her eat whatever she wants and she eats large portions at one time.my niece doesnt like eating fruits and exercising. my mom is big(the best way i could describe it)and other women in our family,but they all were skinny when they were my age(i'm 17) and they started gaining weight after they had kids.now the doctor has her on medicine to help her loose weight,but i think it still wont help unless she exercises and burns her fat.