My Daughter Is 11 Years Old, Friendly And An Honor

My daughter is 11 years old, friendly and an honor student. She has some distant friends but no one on one good friend. She has told me people call her "weird" because she acts silly. She spends a lot of time with her 17 year old sister, to the point she has told her she is "very sad when she isn't there". My 11 yr. old is following in the shadow of a popular, ambitious sister. We are just worried about her naturally, and wonder if this is something to worry about or if we are overreacting.