1) Mucosal injury (internal lining of pharynx and esophagus) may be caused by potassium chloride tablets, nonsteroidal anti-inflammatory drugs (NSAIDs), or antibiotics (doxycycline, tetracycline, clindamycin, trimethoprim-sulfamethoxazole).
2) Pharyngeal diverticulum
3) Peptic strictures due to reflux
4) Benign esophageal tumors
6) Esophageal Stricture or constriction
7) Globus; a psychological phenomenon of something causing difficulty in swallowing (there is a condition called as Globus sensation, which may be responsible for the symptom of problem in swallowing). Please read this resource;
Globus is quite a common phenomenon and many times can be associated with anxiety.
Following investigations are necessary for the work up;
1) Fiberoptic endoscopic evaluation of swallowing and upper gastrointestinal endoscopy. This has been done for her.
2) Esophageal manometry (pressure study of the food pipe).
3) CT scan
4) Barium swallow
This will give you the exact cause of your symptoms.
I would be happy to assist you further, if you need any more information.