It is quite logical to feel that someone with Alzheimer's (AD) might eventually forget how to breathe as each bodily system slowly begins to shut down. The important thing is
that you have done what is necessary to clarify the cause of your aunt's shortness of breath - you have sought professional medical advice. When our good physicians say that a patient is "OK", I suspect what they are not adding is, "for her advanced age and and the physical maladies that accompany it". Truly, when all things are considered, it does seem that she is doing well. It is to be expected that as the disease progresses the infirmities that accompany old age will be increased and perhaps even hastened and that includes simple acts of daily function. Since breathing is an automatic response to living and not a learned behavior, when she is panting she is most likely just plain exhausted. You sound like a caring niece who has done all the necessary follow up. She is lucky to have you in her life. Take care of you.
Take care of you.