Girl's Behavior

Are shy girls always so confusing to understand?

So there is a girl who is shy and she is my friend. Every time I try to talk to her she is very soft spoken around me. She is so soft spoken with me that sometimes I can't really hear her because she is really quiet. In addition, she does not give me eye contact but seems to be fine with me being around her. Whenever I talk to her and ask her a question, she replies back to me but seems shy about it. There was one time when I complimented her, she looked down, blushed, and said thank you with a really soft spoken voice. Because this was not the first time I got confused about her behavior, I asked her friends about it and one of her friends told me that this girl is not shy around her but is soft spoken. I immediately started to wonder why she was not shy around her friend but really shy around me. In addition, the other day, I was sitting and talking with her and one of her friends came over and started talking to her and she suddenly became a little bit more animated but still soft spoken around her (the same friend mentioned above) before going back to being shy and soft spoken around me. So is she interested in me or does she not want me around? Also what are the signs a shy girl is interested in someone and what are the signs that a shy girl is not interested in someone?
Are shy girls always so confusing to understand?
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