Yes it sucks when you have a friend who might be interested or she is interested in your friend. I've been there and I absolutely hate it, which is also why I never do that to my friends. I try to keep them away and sometimes it works, but don't be too obvious about it.
The are lots of women who like having guys as friends. If you ask them, they will tell you that guys give them less problems (women can be very bitchy among each other) That doesn't mean they don't like the extra attention. Even among men, we all try to outdo each other among ourselves. However, she hasn't gone overboard by blatantly flirting and leaving you in the high and dry (women like that exist and they don't realise that they're doing it). Her actions are very normal - calling you up, hanging out together, going to parties etc.
But eventually, she's gonna have to like someone. Question is whether that's going to be you or someone else.
I see two strategies here for a girl like her:
Strategy No 1 - As what the rest of the guys have been suggesting, don't sit around and wait for things to happen. Do the right things.. date her, take her out, make it obvious that you want to be more than friends. I would stop short of "confessing" - it will be quite obvious if she already had interest and I think she doesn't yet. But if you start asking her out alone, sending her flowers etc, she might think again and start seeing you differently. Of course, the risk here is that she could say no and you'll never see her again.
Strategy No 2 - be a good friend. She may fall for you. Since she's the type who likes hanging out with friends (and from my experience, girls like that like hanging out with gays cause they are harmless) I think you can put yourself in her life this way. Once she finds you "harmless", she will be more open and will seek you out more often. Obviously, don't start telling her you're in love too early and don't act wierd when she's out with her friends. The risk here is a very broken heart if she decides to confide in you about other men. But you never know - she might just turn around one day and ask you why you've never gone after her like the rest of the men - and thats your cue then.
Good luck. Personally, I'd take Strategy No 1 because it can be less painful, but then it's also cowardly. I'd advise Strategy No 2 because that's long term thinking if you really like the girl.