Yes it can spread internally, I'm sure some of the members will explain more about that as they see your post.

how did her RSD spread pattern wise on her body?
it started in her foot?
did it mirror to the other foot/leg or go up the side to her hands/arms?

Does she have the swelling/mottling/color & skin changes/ extreme sensitivity to touch & breezes in the areas you can see?

Did she have an MRI that shows no issues at all going on with her spine?

I'm just asking as some of the symptoms you mention - hand use, breathing, dizzy, swallowing can also be symptoms of thoracic outlet syndrome (TOS)

Is she using the computer or video games a lot?
any previous car accidents/ sport injury/ falls?
How is her upper body posture?
Is her head /shoulders hunched or rounded and forward of the body?

Could she be having muscles spasms in the upper body or trigger points?

TOS is also very tough to get a firm dx on and many drs will poo poo it as they are not knowledgeable on it.

If any of that sounds like it might be a fit, an expert/advanced PT should be able to do a comprehensive evaluation for it - they have much more study of the body/structures than most MDs.