OP - I'd just ask the co worker to stop coming into your office immediately after smoking because of your medical issues. Most smokers are pretty considerate and understand.
If she's following the policy the company has in regards to smoking there really isn't anything else you can do.
Good luck with that. I certainly wouldn't want to be 'that' employee.
They aren't lepers. If they're following the guidelines put forth they have just as much right to smoke as you have in your choice not to. I have a hard time with smoke as well, but if she's following company policy she's not doing anything wrong.