It really depends on what kind of girl she is. First you must ask yourself "is she shy?" If shes shy it will be harder to tell if she likes you. But she will still show signs. If she stares at you, often, and then look away as soon as you notice, she most likely likes you. If shes not shy, she will give you signs a lot more noticeable. She may try to talk to you a lot, and try to sit next to you. Try asking her to help you with something, and if she helps, she probably likes you. If she doesn't, maybe she is just shy. Remember, if a girl has a big crush on you, she might not want to do stuff in front of you, in case she embarrasses herself. So good luck!
she will probably ignore her friends a little bit to talk to you, she also might flirt with one of your friends a little bit but not to much... if you want to date her then just strait up ask her if she likes you