Hey,
I am sorry to hear that both you and your siter have been unwell, though it is very fortunate that you have each other. It can be very hard for someone to ever imagine that some of the symtoms of an anxiety disorder can be so painful, physical and real. Sometimes there are no thought problems, OCD symptoms and the disease can sometimes come across as just PHYSICAL SYMPTOMS.
I really think if your sister would like to keep searching for an answer she should go a head ,BUT in the mean time while she is looking she should definantly try some treatments for anxiety. Whether it's medication, seeing a psychologist or even talking here online etc...... "it can't hurt", and it may not be anxiety after all but until she tries some anxiety treatments she won't know.
Unfortunatly we can't help the name of the illness we have, and if the doctor told you that you have a cold and cold tablets would help -you would try that. So the best thing to do when a doctor tells you it's anxiety and the doctor has treatments to help, the best thing to do is give the treatment a go.
So good luck
xx Skye