my husbands sister doesn't like me ?

So I've always had a bad vibe from my husbands sister .. (she's 19) I love observing others and I just always had a feeling she didn't like me or was judging me . I understand why she would judge, I mean I'm married to her brother .. but I'm so friendly to her. Today I went to a get together and my husband and her with some others got a table together. And she would constantly pull him outside to talk to him. This is my first time meeting everyone else in his family . Soo it was quite awkward because I didn't know anyone. Anyways.. he later on told me that he doesn't like how she looks at me . He believes that she has something against me. How would you feel? What would you do