Friendships are reciprocated. If it seems to be one-sided then I wouldn't even bother with the friendship to begin with. You say she's a great friend, all fine and dandy. Have you asked if she's seeing anyone? If you don't have my luck she may not which gives you the opportunity to ask her out.
Don't be pushy and insist or it'll really put her off. Be cool about it. On the off chance she declines for any reason it may not necessarily mean she's not interested though, so ask if she's available any other time. After all if you're not given a definite answer (i.e. "Sure!", "Yeah!", "Not really, no." and "Sorry but I'm just not interested.") the battle isn't over.
Don't be pushy and insist or it'll really put her off. Be cool about it. On the off chance she declines for any reason it may not necessarily mean she's not interested though, so ask if she's available any other time. After all if you're not given a definite answer (i.e. "Sure!", "Yeah!", "Not really, no." and "Sorry but I'm just not interested.") the battle isn't over.