Ariel clearly thinks her opinion matters much more than it really should.
Imo, this is a lack of respect for you as a rider. If you can fix the respect issue, this should go away on its own.
Things that you can do to establish and maintain respect:
* insist on obedience on the longe - the longe line is GREAT for establishing respect. If you can get her to the point where she will longe like a dream, that should carry over to under saddle work as well.
* keep a steady contact. The steadier the better. Every bobble in the contact is an opportunity for her to do her own thing.
* practice lots of frequent transitions. w/h/w, w/t/w, t/w/t with only a few strides between each. She needs to willingly comply with what you're asking her to do WHEN it's asked. Also can do transitions within gaits - put two poles down a set distance apart and then count trot strides between them. When you put your leg on, there should be fewer strides between the poles than her normal working trot.
* practice lots of figures. Circles, serpentines, figure 8s, changes of diagonal, etc. Keep her guessing and at no point let her opinion of what's happening impact your agenda.
* leg yeild (not sure if you're doing this yet but if you're not there's no reason you can't start). go two strides one way, then two strides back, etc.
* Ride with a purpose - have a (flexible) plan for your ride and stick to it.
Hope this helps.