is this a healthy weight?

so my little cousin is 10 years old, 5'2 1/2 and she weighs 132 pounds. she is really strong, and muscular and her bones are HUGE. she could break your nose with the strength of a playful punch to the arm . her dad is 6'6, and weighs about 300 pounds, half of it literally muscle. her mom is 5'9 and weighs about... i'd say 190. my cousin keeps on stressing about her weight. She keeps saying she's fat, she's said it like, 10 times in the past 2 days and the other day, i caught her starving herself. I can see it in her that when she sees a skinny, little 90-pound 20 year old she is comparing her self to the woman. I know that her doing this is not good for her, and i also know how she feels and it saddens me that she has to go through this because i was doing the same exact thing, and i know the thoughts that run through her mind/ she likes this boy and has for...3 years? 3 years. and i think it might have some thing to do with her bashing on herself. i just wanted your opinion. thanks. loves, hailey