My co-worker who I share an office with is passivley rude, how should I respond?

When I arrive in the morning and say "Hi", she ignores me and same thing when I say "Bye"..she will offer snacks to other co workers and not to me. She sparks conversation with others and not me. She does not have the guts to be overtly rude with me (probably because she has no real reason to) She is "nice" otherwise, but I know she secretly does not like me. I am just darn curious as to WHY she wouldn't like me...I really want to ask her what is her problem...she has only been working here for 3 months and has built friendships with others and she refuses to even look at me..what does this mean?