^^ Good post.
Also, have you established forward motion from the ground and use a consistent cue like words or smooching that would easily transfer to the saddle?
When I have a young horse that is "stuck", I will generally take up one rein and bump with the outside leg while smooching and if that doesn't get their feet moving, a gentle pop on the outside butt (away from their head) with a bridle rein will usually do the job. But be prepared for a big jump if you use the rein and have never done it before.
Don't get frustrated, many young horses go through a stage like this. As long as her feet are moving, then you have control and it will just take some time before she figures out that it is more comfortable to line out and trot a bit as opposed to turning in little circles. Just keep at it and don't give up. ;)