What can my wife do to alleviate her constant knee pain?

Mthr is on tramadol for arthritis and our doc said he was not concerned about her getting hooked on them but relieving her pain.

How overweight is she? I know people who are overweight (medically they are morbidly obese) who have had the surgery. They are 20+ years younger though.

I second and third the suggestions for PT.    There may also be an exercise she can do on her own, if approved either by a ortho, psychiatrist or other treating doctor.

https://www.globalindustrial.com/p/medical-lab/physical-therapy/exercise/global-153-pedal-exerciser-silver-vein-knocked-down?infoParam.campaignId=T9F&gclid=EAIaIQobChMIi7SnyMCA5QIViv7jBx3Uag-3EAQYAyABEgJb6_D_BwE

They're called "pedal exercisers" and can be used by both hands and feet.   Rehab facilities have more expensive, heavier versions.    The home version runs about $15.00.  

The question would be though if she's able to move her knees, and comfortably, enough to use the bike while it's on the floor. 

My father used one of these, exercising while sitting in his chair reading.

Not a lot. I know you will have heard the one about "overweight" and likely your wife has as well, and we all know it may not be likely she will address that. And even if she DOES address that, she is bone on bone and that is excruciating. Now it is on PT visits to see what she CAN do given she will not be having surgery. Ask the doctor for PT specialist in this. They can recommend what assistive devices are best from walker to braces to whatever. The cortisone is the best they have. There will likely need to be pain evaluation treatment. Your wife may become addicted to pain killers and there may be no way around it; the prime imperative is that she doesn't fall because of either pain or too many meds.
Your wife is facing immobility and wheelchair at this point, because at this point it is either that or a total knee surgery. And the latter is not on offer.
Again, on the weight. Have you asked the surgeon "If there is less weight can she have surgery, or is surgery still out due to medical issues?" That may take the weight off the table as an issue. Or may give incentive that if there IS weight loss there may be surgery and less pain.
So very sorry. There are few things more depressing than constant pain. Docs are afraid of opioids and giving them now to the extent they will often not prescribe when they SHOULD. The pendulum swings one way, then the other, and seldom stays in the middle common-sense area.
So sorry.

Ask her doctor to write her a script for physical therapy. PT will allow her to strengthen the supporting muscles. The PT may also recommend a brace. There are topical pain relief gels. Does she ice her knees? This helps too.