My sister (17) is obsessed with the Vikings series and what should we do?

To be honest me and our parents does not like her obsession due to the violence and sexual themes in the series. Especially she is obsessed with the character Ragnar, she even wrote a song about him and ships herself with him. Also she tries to look like a warrior when she going out and wear a warpaint like makeup, and our parents doesn't allow her to go out like that (she is crying right now because they didn't let her) and she wears weird jewelry all the time. We don't know what to do, this girl is obsessed with the viking stuff since her childhood so i can't be surprised about she like that series. Me and our parents want to stop her but I do not want to make her sad.

My sister (17) is obsessed with the Vikings series and what should we do?
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