OP – Attention, sensible useful advice follows.
I’ve been in your position. Faffed around for ages ‘being friends’, then got fed up with that but carried on, moped etc. Then realised that the friendship was over as soon as I realised I was no longer happy with it. Therefore asking her was the only hope of remaining on good terms, either by getting it on or getting it out in the open and getting over it.
Therefore you MUST, for her sake if not yours and ours, MTFU, grow a pair etc. and just ask. Forget the face-to-face thing if she keeps cancelling. If nothing else she’ll be flattered. Worst case it’ll be awkward. Give a sh*t? It’s better than what’s going on now.
(For the curious, she said no in my case – natch – but we got over it and I could go back to listening to watch she was saying rather than thinking about what might be. And stealing furtive glances.)