Does anyone know what's wrong with my Easter Cactus? She's very old (at least 40 yrs) and over the past several months has been developing these odd purplish markings on some leaves and then the leaf drops off. Was repotted about a year ago with succulent soil and has good drainage. I'm terrified she's going to die. Attaching a photo of what the leaf looks like when it drops and of the entire plant (front plant in photo). Note it's (baby) sister plant sitting right next to her is doing beautiful and gets the same exact treatment.