Why is this happening?

There's a girl who constantly stares at me all the time and when I look back she pretends like she was never looking. At first, it was kind of weird, and I started paying more attention to her. She turned out to be really nice, and I think I might in fact like her. She's not exceptionally pretty, but her personality and passions stand out. We share a common interest, but I don't know if I should make the first move, or if he she even likes me, since I've noticed one of her friends is stalking me. Maybe I'm overthinking things. But I can't have two girls constantly staring and at me and stalking me, it's kind of weird, and every time I try to talk to this (first) girl, she shyly avoids me and looks down to the floor, unless I directly ask her something. Even when starting a general conversation, everyone talks to me, but her. Even her friend. And she literally talks to every single guy openly but me. Once I tried to start a conversation, but her friends just burst into laughter, and she looks away. I don't know if it's some secret or I just look like a clown.