I hate to hear that someone so young has to deal with this.
I have full body RSD/CRPS. It started in my right shoulder.
I have breathing problems. The first time it happened my chest got tight and breathing was difficult. After going through all the test it was determined it must be from my RSD.
When I get anxious or eat a large meal I notice it a lot more. I get short of breath just holding my breath to wash my face.
For me it's been a mind over matter situation. I have to stop what I'm doing and concentrate on the quality of my breathing to help it improve. Sometimes at night when it's real bad I sleep in the recliner in an upright position.
I hope things improve very soon for your daughter.