Hi Sara.
How are you doing?
Nipple discharge can either be caused by a benign or malignant condition. Since your mother’s nipple discharge involves one breast, the underlying pathologic condition should be sought. Benign causes include fibrocystic disease, mastitis, and breast abscess. Malignant conditions that can cause nipple discharge include breast carcinoma, sarcoma, and Paget’s disease of the nipple.
It would be best to have your mother seen and examined by a doctor for full evaluation.
Good luck.