If you are another female that she finds nothing in common with, she may not want to encourage you to start hanging around like a friend.
If you are a girlfriend of hers and she makes sure you only see her hug others, then she may be pissed off at you and wanting to hurt you back and this is how she is choosing to do so.
If you are a male and you only see her as a friend, but she feels for you as more than a friend, she may not want to hug you because it gives her false hope so she is distancing herself from you.
If you are a male who likes her and she is your girlfriend but the relationship fairly new, she may not hug you in public because she fears teasing from her friends so she just doesn't hug you.
If you are a straight male and she really likes you, she may feel too awkward approaching you yet because fear holds a person back from even something simple as hugging a person but afraid of making herself appear foolish to you and fear of saying or doing something stupid so she doesn't hug you.
Attention: NOTHING on this site may be reproduced in any fashion whatsoever without explicit consent (in writing) of the owner of said material, unless otherwise stated on the page where the content originated. Search engines are free to index and cache our content. Users who post their account names or personal information in their questions have no expectation of privacy beyond that point for anything they disclose. Questions are otherwise considered anonymous to the general public.