How bad is bladder cancer for an 85 year old woman?

It depends: Bladder cancer has variable severity. High grade cancers which invade deeply into the bladder wall carry the highest risk, whereas some cancers are "low grade" and less invasive and are not associated with risk of metastasis, but can recur frequently. In reality these are different diseases but both are called bladder cancer. This is analogous to skin cancer, eg, basal cell vs. Melanoma.