I hate my sister. She's always so fake and happy. Is something wrong with me or her?

Hate your sister? Most people go through periods of conflict with their siblings, even feeling hate for them at times. But when the going gets tough, one's siblings can be a big support. You might look at what you're specifically hating about her ["so fake and happy"] and see if it corresponds to some quality you would like to have for yourself. [maybe the "happy", not the "fake"]. What would make you "happy"?
Hate feelings. Possibly you are having a psychological problem behind your hate feelings. It is important to get help with this as hateful feelings unchecked, can cause you damage to your mental health. Talk to your parents and your doctor about these feelings to find help.