I'm going to guess that this is going to get some not so good feedback, buttttttt.....
Moving away and not letting you mount is just that, the horse is not giving you permission to get on his back whether it she is frightened or just doesn't want to get worked. Either way she is not comfortable with you up there.
In the wild, where does the lion want to go on the zebra? The back!
Bring her up to the mounting block and just stand there, petting her. How is her reaction? Is she jigging around? Is she still trying to move? If no then just continue to pet her...if yes then get off the mounting block and then start petting her and playing the friendly game with her.
Next step would be to jump up and down like you were going to mount but not actually mounting, while still petting and being friendly. If the horse still moves, let her move around you (this should be done with a halter and lead rope on...about a 12 foot lead rope is best cause it gives you more room and her more room to work with) as you continue to jump. When she stops moving you stop jumping :) Work on this so you can jump up and down on the mounting block and she is not bothered nor does she move :)
Next step would be putting your foot in the stirrup and jumping up...now this can be difficult if she walks away, and what you'd have to do is take your foot out of the stirrup and continue jumping up and down.
Then stand up in the stirrup and face her (your belly button is towards her head not to the other side), but do not swing your leg over.
Then you'd go and lay accross the saddle (or bareback ...bareback would be more comfortable).
Then the next step would be going up, sitting down, then going back off.
Each time backing off if she is uncomfortable or in the case of the jumping, continue until she stops :)
All of my horses have gone through that if they started walking off, I've never had a problem after doing it once ;)
And sorry if it's confusing, I wrote this very fast :)