So what if all she said she wanted was friendship. Women don't even know exactly what it is that they truly want. It's up to you as a man to lead her where you want her. My ex told me two weeks before getting back together that she had "no desire to get back together with me" and tried to play that LJBF's card. I did the same thing to her mixed with pua tactics and she crumbled.
I would suggest the "hey can you do me a favor text?" When she responds tell her "nevermind, it's o.k.". It will drive her nuts wondering what you were going to ask her. You can keep that one going for a couple of days and it will open the door so you can initiate conversation again. She'll welcome any interaction with you just to figure out what you were going to say. Women love mystery.
When she pushes it again--and she will, tell her that: "I was going to ask you if it could always be this way between us, even if either one of us started dating someone else--that we could always be friends like this. But, I realized it could never be that way forever and that's why I said nevermind... I didn't want to ruin what we now have."
That would be the equivalent of launching a cruise missile directly at her heart. I wouldn't recommend this tactic to people that aren't where you are at right now though.