Am I insane for wanting to charge my sister for a haircut

I’m a licensed cosmetologist and was taught in school to charge everyone, because if not, they will take advantage of you. My sister wants me to cut her hair and I told her this. I wouldn’t be charging her much, but I think it is reasonable to ask her to give me about $20 since I am a professional. She asks like I have lost my mind and am insane for even asking such a thing. Call me dramatic, but I’d honestly just feel exploited doing it for free🤷‍♀️