<< here's my cynical answer.
She's not into you, and this is her way of letting you off easy. BUT, if things don't work out with whomever else she's got her eye on, she's got you "waiting" for her patiently like a little dog. On top of that, she knows you like her, so she likes the attention you've been giving her, and she doesn't want that to stop. Women love attention, it's a fact. She's gonna string you along, keeping you just interested enough until you give up, or she finds someone that she wants to date. You might be the backup, or worse, bub. sorry.
Or Sarah could be right, and I'm a jaded asshole >>