My two best friends are women, and I dated both of them in the past. Both, at some point, had (one has) strong feelings for me, so I can comment on this situation.
Only you can discern your true state as a "friend". Once you have truly become a "friend" in her eyes, there is very, very little chance of transcending that once again. If she feels comfortable discussing dating other guys around you, it seems to me that you've definitely hit that "friend only" state. Once you're there, any sort of sexual conduct seems almost taboo.
One of my friends, whom I dated a while back, had strong feelings for me for quite some time, so we didn't hang out much with each other because it just made things too difficult. It seemed overnight that I acquired the "friend only" status, and I know there's no way I could ever become otherwise. She talks to me about her dates, asks for opinions on what to wear for dates, etc.. We go out, have fun, and that's it. Even thinking of asking her for a kiss seems awkward, and I believe your requesting a kiss from your friend probably made her feel awkward as well.
Having women as friends is a great thing, so don't ruin it.
