Incontinence! Cancer treatments can and do cause different levels of Incontinence. It can also be caused by cancer in that region i.e. Kidney, Bladder, Female Organs, etc.. Depending on your Private Insurance or Government Insurance, different levels of support products can be available (Classification: Medical Diapers). If you have not been part of your wife's medical visits, you need to start. If you have you need to access the visit summation for at least the last coupe of years. If your Medical (Hospital) Group has their records available electronically, that will save vast amounts of time as once you are approved, you can quickly catch-up or at least review with detail.
Upgraded protection is all based around release rate, rate of occurrence, volume and length of time placed in the diaper. High release rate, released often, with a high over all volume and a full night 8 to 12 hours commonly defines a Premium, high volume, night time tab style diaper, likely with plastic pants. Clearly the other far end of the scale would be a light pull-on commonly used to those who drip.
The vast range between those two points has just as vast a list of products. You will need to develop an understanding of where she fits now and with a journal keep track to determine when it become advisable to move up or down based on capacity.
Comfort is a reality as Human Bodies vary as well, add variation from different manufactures and sampling becomes a reality for near everyone.
Hopes this provides a starting point. Understand that you are not alone!!