My sister and I have a question about weight?

so me and my sister are the same age and were both 5'2 ..i know wierd..anyways i weigh 110 pounds and she weighs 119..she has more muscle then me and just because she weighs a bit mroe she thinks shes fat :S ..shes an xs in shirts and a size 26 in pants..i mean i dont think shes fat but i just wanna prove to her shes not so leave any comments good or abd thanks :)