When will the thinking change

literally I have never felt this helpless in my life before...so i have a younger sister (she is 13 years old) and I have fairer complexion and she is duskier...

Aaj hamre guest mai guest aaye hue the and unhone hum dono ko milne ke liye bulaya and the first sentence that the aunty said to my sister was 'tumahara rang to tumhari did se bilkul match nhi karta....tumhe ajeeb nhi lgta apni did ke saath bahar jane mai ' and as usual vo hasi ki hamne to bas aise hi casually bola dil me mat lena...bhai her eyes were filled with tears...and i couldn't do or said anything... it's been 3 hours and she is still inside her room...

I DON'T KNOW HOW TO HANDLE THIS SITUATION....how to talk to her or may be i shouldn't because filhal mere se bada dushman uska aur koi ni hai...