She has difficulty walking, bad knees, bad back and yet mentally 100%. What stage will determine a lot but I'm concerned about her going through any surgery or treatment. How long can we expect no real pain or discomfort? Would it be wrong to simply take minimal treatment so the last years of her life aren't made more difficult?
Both my parents had bladder cancer. This can be a quite cancer but my parents saw blood in their urine. It is cureable if found early. The chemo, live Thurberculosis virus, is put directly into the bladder. Then the person has to turn to side, back, side and back every few minutes. Everytime they use the toilet it must be cleaned completely with bleach since virus is live. The problem comes in when the cancer goes thru the bladder lining. Then surgery maybe needed. So, it needscto be determined how far its progressed and that is done by a scope.
On the issue of repeated UTIs, you mentioned a local doctor. You might want to ask if an infectious disease doctor can be brought in on consult. My father's last two hospitalizations have involved sepsis; each time a highly rated, very good (and also very personable) infectious disease doctor was consulted; he solved the problem.
And talk privately with the attending physician and raise your questions, asking if there are noninvasive ways to test for bladder cancer. (I don't know if a biopsy would be necessary or not, but there might be some blood work that could suggest the presence of cancer cells. I'm just not that knowledgeable on bladder cancer.)
I understand the issue with treatments; we made that decision when my mother was D'x'ed with breast cancer in her 80's. There is a value in knowing though, so that (a) you can identify symptoms and when/if they accelerating or intensifying and (b) you can understand if behavioral changes (such as depression) occur and (c) you won't be wondering what else might be occurring physically.
My Mom had bladder cancer and she would see the urologist every year. My Mom was 90 at the time.... her doctor told me that the cancer won't kill her, it will be something else. He was right. My Mom had passed at 98 due to complications from a fall.
If your Mom's doctor says the cancer is very slow moving, then I would focus on Mom's other health issues, such as her knees. There is now a gel that can be placed in the knees to help bone on bone knee pain.
My mother in her late 80s declined to have further tests to confirm whether she had cancer or not. She told the doctor, "I would refuse to have treatment, so what does it matter if we know the diagnosis for certain? I have had a good long life. I am going to die of something. If it is from cancer, so be it." The doctor respected that decision, as did her children.
Other competent adults would make very different decisions.
If your mother wants to talk through her options and her feelings about them, perhaps you can be a sounding board for her. Her decisions should drive what comes next.