Can somebody tell me what's wrong with my sister?

Alright, here's the deal. My sister is 15 years old. She has a really short haircut. My mom dresses her because she has no sense of style, and therefore, she never dresses in an attractive manner. She has never worn makeup before, she takes a shower every other day, and she does this at nights, so most of the time during the day she really smells and looks unpleasant. She never talks about guys, and shows absolutely no interest in them. She is a complete mommy's girl, she has never done anything wrong or badass in her life, and she ALWAYS snitches on her four siblings, including me, and I'm 18. I always tell her that snitches end up in ditches, but she just doesn't seem to understand. She has only a few friends, and they are complete geeks and nerds and are just like her. So, all I'm asking, is for somebody to tell me that they know what's going on with my sister. Is she lesbian or something? What is wrong with her?