"her PCP is there for the flu, for normal day to day stuff but they don't really handle any of the diabetic issues, which this was a diabetic side effect issue."
That's not why a PCP is required. The purpose of a PCP is to carefully monitor all of a patient's conditions--that means getting copies of reports from all of a patient's specialists, including new meds prescribed.
Depo Provera cautions: "This medication should not be used if you have any of the following conditions: history of stroke or other blood clots (e.g., in the legs, eyes, lungs), breast cancer, liver disease, current/suspected pregnancy, abnormal/unexplained vaginal bleeding.
Before using this medication, tell your doctor or pharmacist your medical history, especially of: asthma, abnormal breast exam, family history of breast cancer, cancer of the reproductive organs (e.g., cervix, uterus), frequent use of alcohol/tobacco, depression, diabetes, eating disorder (anorexia), heart disease (e.g., chest pain, heart failure), high blood pressure, kidney disease, high cholesterol, irregular/missed/light menstrual periods, migraine, personal/family history of bone disease (e.g., osteoporosis), seizures."
Diabetic retrinopathy is a complication of diabetes and you indicate she already was diagnosed with same-did she share this with the gynecologist? She would have to prove a causal link between the medication and this complication of diabetes which she already had.
Literature does state that this medication should be discontinued pending examination if there is a sudden partial or complete loss of vision
No one on a board can possibly guess if she has a case; she needs to consult a medical malpractice attorney who would have a medical expert evaluate her medical history.