I did just think of trying to just keep pushing her from a trot to see if she will just go into a lope. Like start with her slow trot, then extended. ..but just keep asking for a faster trot until she just tries to lope? Instead of asking for a lope like normal.
Downward transitions from trot to walk or stop are great. I don't have to touch the reins. But from her gallop, I one rein stop her, she just fights me otherwise.
I do not think you are going to get any control working at the canter / lope / gallop until you MAKE her respect your reins and you pulling on her.
That being said, the very first thing I would do is have a good dentist work on her. Bit seat may help and a three piece medium weight snaffle would definitely be in order.
I do not care how idealistic one is and how much some riders want a horse to listen to the lightest aids, a horse that is disobeying those aids is not going to go any farther in their training until they learn to back off from the basic aid of 'pulling them up' and 'slowing them down' with pressure on both reins.
I think it is useless to expect any different result when you are just repeating the same scenario. [Some people call that the definition of insanity. Repeating the same thing over and over and expecting different results.]
This horse is not going to gather up and slow down until she learns to tuck her chin and 'give' to bit pressure. Even race horses are taught to gallop properly with a tucked chin and 'bowed neck'.
The main reasons that every horse needs to learn to give to bit pressure is for control (obvious) and to learn to properly use themselves. Only when a horse has its neck bowed and its chin tucked, can it properly use its back and belly muscles. No horse can round its back, get its hind end under it and tuck up and use its belly muscles with its head in the air.
So, like it or not --- idealistic use of light aids that the horse is not obeying, it just teaching your horse that it does not need to listen to any aids at the lope / canter.
I would start reschooling this horse by using either draw-reins or a German Martingale until it could be controlled and pulled up at the gallop with both reins. Once it has learned to tuck its chin, slow down and stop with both reins, THEN I would work at refining the aids. I would gradually ask for more and more refinement.
I would also be doing all of this out in a corner of a pasture and not in an arena. I would quit each session in the arena and teach the horse that the arena is a good place and not a battle-ground. You know you are making headway when a horse is doing something better at the end of each ride. If it is not doing better as time goes on, you need to change your approach, change bits or equipment or ask in a different way. You cannot just keep repeating the same routine and expect different results. It is futile and horse is just getting more practice giving you the wrong response.