I'm going to have to put my pockets worth on this one, better than starting a new thread, after all. You might get something out of it, Ill need a little affirmation though heh.
My advice to you is to go with it. You didnt mention any real baggage to speak of, it seems more like the principal of rebounding to her friend is what concerns you. I'll tell you not to worry about that, I would hate to bring up such an old additive, but all is fair in love and war. If you want it, go for it - and don't let anything stop you (with the exeption of the law, and you know, common sence). In any case, here is my similar story, take what you can from it.
I fell for a girl, and it was a shaky and uneasy attraction that tore me up day and night, and I actually turned to her friend for advice on what to do. I had known this friend before I had fallen for the original girl, but for reasons filed under what I thought to be hopeless, I didn't bother trying.
Anyway. When my little crush didnt work out, it did turn very sour, I completely stopped all comunication with the girl, deleted her phone number, pictures, and stopped reading her blogs. (Which, helped greatly, I will say) However, I was still talking her her friend, not so much as I would a close friend, but more along the lines of an aquaintance.
Well, some friendly gatherings, some group outings, ect, and some very casual online talking actually had her falling for me. The strange thing about this whole position is that she, and the girl I did have an interest in before, are complete opposites. The girl before was rather permiscuous, spoiled, young, and well... stupid. The new intererest, however, is an upstanding, christian, intelligent young woman who actually has many of the same values as I do, and it has sickened me to know that I had actually lowered my standards for a girl that wasn't worth any of my time while a girl in any other situation I would have considered perfect was sitting right there.
I will have to ask this forum, in its great amount of expertise on such matters, what any of your opinions would be? I do like this girl, I certainly do see us being able to work, however, she is best friends with the previous girl, whom I ultimately dispise as a human being. As you can imagine, it is rather awkward. On a final note, I am 19, the new, current lady interest is 16, almost 17. If that age bracket matters, then tell me, because as far as I am concerned, she is very mature for her age, in comparison to some others.