Is my sister a lesbian?

My sister (age 17) has posters of Ellen Degerass tacked up all over her room. She dresses like Ellen and tries to act like her. 1 & 1/2 year ago she cut her hair and has been wearing it just exactly like Ellen. She never had a boyfriend in her life. She flirts with our cousin who is beautiful. She also... show more My sister (age 17) has posters of Ellen Degerass tacked up all over her room. She dresses like Ellen and tries to act like her. 1 & 1/2 year ago she cut her hair and has been wearing it just exactly like Ellen. She never had a boyfriend in her life. She flirts with our cousin who is beautiful. She also thinks she can dance (just like Ellen) and she tries to be funny. She IS funny but she can't be a comedian because our parents are making us go to college after we gradguate high school. We are actually step sisters and the same age (even born in same month) and are starting senior year so we aren't little kids. That's why I'm so concerned about her. She is too old to be copying a celebrity. Everybody at school will think she is gay. What can I do to make her snap out of it?
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