I am so sorry to hear about your mother. This is a very serious diagnosis, especially if it has gone into the muscle, and especially at her age. And yes, while many bladder cancer patients have no idea of what might have caused it, smoking IS the number one identifiable cause.
Hope that she is being seen at a practice that specializes in bladder cancer, particularly in high risk patients (your mom's age puts her in this category.)
If not, you might want to consider getting a second opinion at such a site. If you let us know where you are located, we might be able to suggest a few.
Chemo and the expected surgery are not easy. Which is why you want to be sure she is in the best possible place. And invasive bladder cancer is not something to ignore.
Please let us know how she is getting along.
Sara Anne