When they discover they've got a crush:
It's not something that happens to Karen very often, since it's very hard to capture her attention, but she just goes with it. She admires you from afar and talks about you with other people, always interested in what others around camp are saying when your name is mentioned. She doesn't actually think anything might come from it, but it's fun to indulge in it while it lasts.
How they confess/hint:
Karen is blunt, and with her love for alcohol, it's not likely her feelings for you would stay secret for long. It just depends on whether you put much merit into her drunken confession or not; she does flirt with you around camp rather often, seeking out your company when it's around dinner time or when there's celebrating to do.
How to win their heart:
Be a true romantic. Karen isn't used to getting that slow, romantic shit that Mary-Beth is always reading and writing about, and she wouldn't even be able to admit she likes it until it's happening to her. She'd like someone who knew how to have fun with her, too, without just thinking all about sex (though that's also a fun portion of a relationship).
How to break their heart:
She braces herself from the start for something awful to happen, which is very unfortunate considering this lack of faith can put a damper on any relationship. Being disrespectful or too pushy with her, crossing her boundaries, and acting like you're better than her are good ways to piss her off, too.
Things that make their heart flutter:
She loves when you flirt with her, touch her in cute, intimate ways (like twirling her hair, stroking her cheek, planting kisses across her face). Taking her out on cute dates would make her heart rather fluttery, too, like taking her to see the stars or on a peaceful walk in nature so the two of you could talk freely without interruption.
Their type:
She likes someone with a good sense of humor and good energy about them, who exchanges in playful banter with her without being too crude or annoyingly pushy. They'd need to be bold, to see her 'insults' as just another sign of affection, as she can have trouble properly expressing her own emotions. She'd like having something who's protective of her, but doesn't really step in, letting her handle herself and then doting on her afterwards.
Goals in a relationship:
She's not very interested in kids or marriage, she just wants a partner willing to travel around with her and see interesting sights. She doesn't like to focus too much on the future because she never knows what's gonna happen, insisting on enjoying there here and now for as long as you both can.