Welcome to e health forum.
The description of the CT finding is indicative of a ulcerative and infiltrative lesion within the lower esophagus, which could be a indicative of Esophageal cancer with extension into the upper part of the stomach.
A upper GI endoscopy should be done to get a clear image and samples for histological examination should be done. Based on the findings the exact treatment can be decided.
The treatment options include - surgery, radiation therapy, chemotherapy or a combination of all them. The actual treatment for your mother would depend on her general health, her symptoms, the extent and severity of the cancer and presence of distant spread, etc.
She will need to consult with a Gastrosurgeon who can get more detailed facts and history and provide a proper advice regarding further management.
I hope this helps.