In answer to your question it is not the inside or outside rein that raises the head.
In a rising trot it is the inside leg. In sitting trot it is your stomach muscles and look at the horizon. Same with canter. In walk and canter your hands follow the head. In trot your hands stay still.
The height if the poll becomes higher as the horse becomes more advanced. You don’t expect a 4 year old to go with the same height as a grand prix horse.
The inside rein asks for flexion and then gives. You do not hold your inside rein. If you hold your inside rein you are blocking forward.
Horses will either lean or go with their head in the air to get away from the pain of bad hands.
Curling is more a mistiming of correct contact. Horses learn from release of pressure. If she curls and you follow, you have rewarded her to curl, you have taught her to curl.
Don’t worry contact takes years to learn, you take this as a learning opportunity and as someone above said you really need a great instructor on the ground.
The horse is a mirror. A mirror that shows every pimple and every blackhead! Sigh!
The simple answer of why is she curling, is because you are asking her to curl.
To bop with spur or to lift with inside rein is actually cruel because she is doing what you ask and then is being reprimanded for obeying. That is not fair. Horses teach us that you have to be fair.
With this change she and all horses in your future will blossom.
At the moment if she is curling, then the neck is higher than the poll and she is or will become what is known as broken necked. This is from incorrect riding.
You know this which is why you asked the question. Follow up your own thinking and change and you will go far.
Good luck.