I'm scared of what people will think of me and misunderstand me if i was to use my sister for my art project?

For my art project, i want to use Jenny Suville as my inspirtion, she's an artist that mainly focuses on fat, skinny, hospitalized etc people and paints them in a very effectivie way. I don't know why but i like these paintings ALOT. Anyway since i cant copy her ideas and all i was thinking instead of doing fat/skinny/hospitalized people, I should do people with distorted faces, for example my little sister has a distored face she had previously sufferd from a tumer, leaving the left side of her face to sag down and swell up alot, shes also cross eyed and has one blind eye, the real reason in which i want to do this is because i want to show her in a way that will seem positive? I just want advice i mean im going to explain this to my teacher and im scared that she may think im a horrible person for using my little sister, people wont realise that i want to do it for the good reasons, but i just cant put what i feel into words, i dont know what to do, shes 7 years old i dont want her to see it when shes older and think im a horrible person, please give me your honest opinions because my decision lies upon the opinions gatherd by asking alot of people, thanks guys, appreciated and thanks in advance :)