What is the survival rate for someone with stage 4 ovarian cancer that has spread to the brain, when she is 84?

Unfortunately, low. Stage IV ovarian cancer unfortunately has a very low survival rate. The five year survival rate for this stage is around 11%.
Stage 4 ovarian CA. The statistics for stage 4 disease are, in general, a 17.5 % 5-year survival rate for all patients. No one can predict the outcome of an individual patient, however, and her outcome depends on the location and size of the brain metastasis, among other factors, such as her general state of health, immune status, nutrition, and cardiac status.