My daughter doesn't have a life?

My 16 year old daughter is introverted and never wants to socialize with anyone outside of school. She only has a few friends. When she doesn't have any homework, she reads books on her Kindle. She stays up late reading all the time. Sometimes I get up in the middle of the night and walk by her room and see her reading her Kindle. All she does on the weekend is curl up in a ball on the sofa and read her Kindle all day. She reads pretty fast, and she's read 400 page books in one sitting. She always turns down her friends' invitations to hang out. She takes her Kindle with her in her purse everywhere she goes. We went on vacation a few weeks ago, and she took her Kindle and laid on the beach the entire day reading. She never goes to parties or anything. I know it's a good thing that she's not getting drunk or pregnant or things like that, but I'm still worried about her social life. She never wants to socialize outside of school.

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