Most Helpful Girl
Well it's not just up to her to make a relationship happen with you, it's on both parties.
However, seeing as you two did have some sort of chemistry that she was clearly aware of, going after one of her friends is not only in poor manners, you are likely going to be labelled a dog and she'll make sure that girl friend of hers knows. You can't date within your original interest's friend group without totally pissing off your original interest and causing severe drama - it's just one of the taboos of dating etiquette.
Most Helpful Guy
then she likes u... otherwise i see no point being upset basically...:-)