She's just probably attracted to you.
How to tell if she's even interested:
you're sitting somewhere behind or to the side of her she will not turn/peak out to look at you=she likes you. Sitting in front of her doesn't count therefore the look may be just because you are a moving object in her line of sight or she doesn't like you and sees a face she despises and day dreams bad things to you. If she isn't interested she will not look at you if you are far behind or to the side of her because she doesnt want to lead you on. But it sounds like she is looking at you no matter where you are located, so good news to you! She is attracted to you!
She may even laugh extra with her friends then look if you see her being "cute" in this giggle state.
I also am guilty of starring (like really starring creepily) at people I find attractive. Us cancerians are quite visual and have intense emotions, so she's probably so scared she'll come on too strong because she desires you, thus the no smile creepy stare.
She's also constantly evaluating if you are worth investing emotions in.
Here's what to do:
She will not start a conversation with you, she may fantasize about it but you have to do start it. Be casual, warm, sweet in speaking to make her feel comfortable to get to know you better and calm her nerves. Cancerians are goofy and child-like at heart forever so mirror this type thing. Be kind-hearted and genuine in showing her your character (a cancerian can sense a fake by strong intuition). Share good child-hood memories (cancerians are really nostalgic) I'm sure she'll fall for you.
Just be careful:
Just treat her with respect and don't lead her on because as I said intense emotions. Cancerians can do crazy **** if someone backstabs them. If you ever need to part ways with her, do it respectfully and suggest that you'd be better as friends (still kinda there for her emotions, lol but not really, its a kind excuse to resume to before a relationship started)
Cancerian in a relationship:
Nurturing but not clingy. Goofy, understanding, very giving, needs communication and reassurance on your feelings for them. I find anyone who gets to know a cancerian gets addicted to them because we're awesome!lol
I'm a Cancerian Girl who is really in sync with what I want and feel