Hi ! At this age the muscles do become weak and there may be some difficulty in swallowing, but it will not be a absolute stoppage of food. She is gagging up because the food/liquids what she takes can not pass through the esophagus
due possibly to some kind of organic obstruction and rather gets into her wind pipe. The treating doctor has taken a biopsy
of the esophagus to exclude any pathological cause of the obstruction.
I wish her an early recovery.