She was on that drug for 10-odd years before going to a different hospital on a whim. The new doctor concluded that actually the Lupus wasn't even active. It was in remission and had been for years. Turns out, the previous doctor was skipping some routine tests because the results were always the same.
Mom got off the drug and her mind got better but her body didn't. Off the drug, she was basically in the same physical state as she was on the drug. Couldn't walk or even sit down for more than a couple hours without pain. So what's going on? She started getting her bones checked to see if there was some kind of alignment problem. There was some old film of her as a toddler that showed her walking funny, and she also once had a bad accident doing sports, which seemed like potential evidence for something skeletal.
Before she could figure anything else out, she found a lump and got diagnosed with cancer. It originally looked like regular breast cancer but the breast cancer chemo didn't work. Turns out it's this super-rare "meta-plastic" cancer that nobody at the hospital had ever seen before. She just went through palliative care and hospice then died only a year after finding the tumor.
Turns out there were some studies saying the drug she was on for longer than necessary is correlated with rare cancers. Unfortunately I don't have the name of the drug or the details of the cancer on hand right now. Anyway, it's cool to see some research that might eventually help Lupus patients avoid getting yelled at for popping pills (even when not actually popping pills).