Is it wrong to be kind of upset at my sister for this?

Well in either case you should try and take care of your family. They aren't around forever and neither are you so enjoy it while it lasts( I think this is a good mindset to have). In either case, i know sometimes you want to be alone as well so you have to slowly let her know that things change and that she can't always be with you(be easy about it though because if its too strong she might take offense and leave the college/choose another or be upset at you for a while, etc.) In the end, youll both be fine and its nothing to worry about at all.