I don't think you really need to do anything - other than be civil. You're not obliged to be her friend and clearly she's had the same thought. This can happen at the beginning of college, people will cling to each other whilst they're getting used to their surroundings but find out that actually they have little in common or don't really like each other. It's normal - and also a pain to deal with. If you don't want her friendship - carry on and find others, all that wasted energy thinking about her could be spent finding others who will want to know you.